Sharp differences emerged between the US and Israel over the settlement issue on Wednesday - one day after Prime Minister Binyamin Netanyahu concluded his first official visit to the White House - with US Secretary of State Hillary Clinton calling for an absolute stop to all settlement activity and sources close to the prime minister saying the terms of a settlement freeze still needed to be defined. The settlement issue was expected to be one of the top ones dealt with in working groups that have been set up between the US and Israel to discuss a wide range of topics. Israeli sources said work in these groups had already started. Netanyahu, upon landing at Ben-Gurion Airport on Wednesday afternoon, said four groups would be set up to deal with the following issues: Iran; strategic issues between the US and Israel; the diplomatic process; and bringing other Arab countries into the process. "We want to see a stop to settlement construction, additions, natural growth - any kind of settlement activity," declared Clinton in some of the Obama administration's clearest comments to date on what it expects from Israel. She was speaking to Al-Jazeera in an interview, of which the State Department released a transcript on Wednesday. Netanyahu indicated on Tuesday that the settlement issue was still under review and that its details still had to be worked out with the administration. Senior officials in Netanyahu's office said the exact terms of a freeze would have to be worked out, since there had been a number of unwritten understandings on this matter with the previous administration. For instance, Israel has been working on the assumption that, with tacit agreement from the US, it may build inside the lines of existing settlements in the large settlement blocs that it believes it will retain under any future diplomatic agreement. It was telling that during his two-day visit to Washington, which concluded on Tuesday, Netanyahu made no commitments on settlements, despite the primacy the Obama administration has placed on the issue. According to former US ambassador to Israel Martin Indyk, writing on The Daily Beast Web site, "Netanyahu was completely silent on the settlements freeze in public; in private, I'm told, he said it would be difficult to do." In a conference call with US Jewish leaders following Netanyahu's meeting with Obama on Monday, a senior White House official said the administration was still waiting for a reply from Israel on settlements. "This is the focus of the early step they are looking for" from Israel on the Palestinian front, said one Jewish official on the call, adding that the White House had indicated it was looking for a response soon. "The fact that they were suggesting there was some kind of time frame in the near future suggested that this is a form of pressure on Israel to come back with something," he said, though he also said that "they're not at the point" of imposing consequences should Israel fail to comply with the administration's demands for a freeze. Netanyahu, meanwhile, said publicly for the first time, upon his return, that he would be willing to begin negotiations with the Syrians, as long as there were no preconditions. In Washington, he stressed that he was willing to start immediate talks with the Palestinians. Senior government sources said the US had pressed Netanyahu in the meetings to begin such immediate talks. The prime minister also said upon landing that various strategic agreements that were essential to Israeli security had been reapproved by the Obama administration. He did not provide any details. On Iran, Netanyahu said the US and Israel agreed that "the goal of joint Israeli-US policy was to prevent Iran from developing a nuclear military capability. Obama also said that the engagement process is not unlimited; I appreciate that and think it is a very important statement. There was also an understanding that Israel reserves the right of self-defense." Netanyahu said there was agreement with the US on the need to "widen the peace process to other Arab countries, so that not only does Israel have to contribute, and the Palestinians have to contribute, but the Arabs have to give something concrete, already in the beginning of the process." Israel did not publicly propose a new Middle East diplomatic plan in Washington because of a fear that any such plan would automatically be rejected by the Arab world, senior sources in the Prime Minister's Office said on the way back from Washington. According to the sources, Netanyahu left Obama with a direction of where he intended to take the diplomatic process. The government's hope now is that Obama will raise these issues - foremost among them the idea that the Arab world needs to start making gestures toward Israel - with Egypt's President Hosni Mubarak and Palestinian Authority President Mahmoud Abbas next week. The underlying logic behind this is that the Arab world and the Palestinians would entertain these ideas only if they came from the US, and not from Israel. According to the sources, one of the key topics of discussion between Netanyahu and the senators and congressmen he met on Tuesday dealt with the definition of Palestinian statehood. The prime minister's position is that he cannot come out in support of a Palestinian state - something the Obama administration has done and is urging him to do - without first defining what a state means, and what aspects of statehood the Palestinians would be denied - such as the ability to muster an army, enter into treaties with other countries and have exclusive control of its borders. Participants in the conference call said the senior US official had stressed that the two countries were not that far apart when it came to the essence of the issue, as Netanyahu had backed Palestinian autonomy so long as it was demilitarized with other security guarantees. "They really share the same goals. They may have some differences of opinion about how to achieve them, but this discussion was more about those shared goals," said another official on the call. Another participant said the White House had talked about obligations that the wider Arab world had to contribute toward regional peace efforts, noting that while Israelis and Palestinians had obligations under the road map - the former's including freezing settlements, removing outposts and improving Palestinian freedom of movement - Arab states had an obligation to press forward with the Arab peace plan. That document calls for normalization with Israel in exchange for a full withdrawal to the pre-1967 borders, as well as arrangements on the Palestinian refugee issue that are currently unacceptable to Israel. The US official noted that the Arab states' obligations weren't spelled out in the road map, where Israeli and Palestinian obligations were detailed. This was the closest he came in the conference call to implying that the current framework for peace negotiations should be revised. "They're trying to hint that the road map was incomplete or lacking a component," the Jewish participant said, suggesting it shed some insight on what the administration might be working on as it develops its own Middle East peace plan. Media speculation on the topic was rife after Netanyahu mentioned in a briefing with Israeli journalists on Monday that Obama had mentioned he would unveil such a plan in the near future. Despite reports that its details would be unveiled when Obama made his long-anticipated speech to the Muslim world in Cairo on June 4, the US has repeatedly characterized that address as focused on outreach to Muslim world, and officials said that in any case the speech was currently only in draft stage. Though it could likely include reiterations of Obama's call on Monday for Arab states to take steps on the road to normalization with Israel - as well as for Israel to freeze settlement activity - officials have suggested it would be the wrong venue and too short a time frame for a major initiative to be unveiled. Another option for putting out such a proposal could be at the Quartet meeting scheduled for later next month. Participants termed the exchange friendly and professional, and said the White House also characterized the conversations between Obama and Netanyahu as constructive and beneficial. "They were explicit that the tone and nature of the discussions was very positive," one Jewish leader said. "There was no bickering. There was none of the Bibi-Bill Clinton behavior that was such a mess." Similarly, several Jewish leaders - many from the same organizations - who participated in a meeting with Netanyahu at the end of his trip on Wednesday characterized the encounter as warm and positive. "The mood was very good," said Nathan Diament, director of public policy for the Orthodox Union, adding that Netanyahu had described the meeting with Obama as friendly, productive and long - the encounter ended up lasting four hours. "He told us that the meetings with President Obama went very well. He was very happy, and told us that Obama is exactly on the same page as Israel when it comes to Iran not obtaining nuclear weapons," said Mort Klein of the Zionist Organization of America. Klein noted that in addition to being willing to negotiate with the Palestinians, Netanyahu had also expressed a willingness to talk to Syria as long as there were no preconditions. The Obama administration has also been reaching out to Syria and supporting efforts for Israelis and Syrians to restart third-party talks that faltered late last year. E. B. Solomont contributed to this report.