As the deadline set by the UN approaches, the US is pushing for swift sanctions against Iran for its lack of compliance with the international committee's demand to stop its nuclear enrichment program, American officials said Monday. Iran is expected to provide its response to the European incentive package on Tuesday, but the US is looking ahead to the UN deadline set August 31. Sources in Washington speculated that the Iranian response to the incentive package would not be conclusive, yet would include no sign of willingness to stop the uranium enrichment process. US President George W. Bush said Monday he hoped the international community moved quickly to impose sanctions against Iran in case it decides to go ahead with its nuclear project. "There must be consequences if people thumb their nose at the United Nations Security Council," he said at a White House press conference. "We will work with people on the Security Council to achieve that objective." On Monday, Iran's supreme ruler Ayatollah Ali Khamenei said Teheran would continue to pursue the contentious nuclear technology. "The Islamic Republic of Iran has made its own decision and in the nuclear case, God willing, with patience and power, will continue its path," he was quoted as saying Monday by state television. Khamenei accused the US of pressuring Iran despite Teheran's assertions that it was not seeking to develop nuclear weapons, as Washington and its key allies contend. "Arrogant powers and the US are putting their utmost pressure on Iran while knowing Iran is not pursuing nuclear weapons," he said. On the eve of its expected answer, Iran also took another step to make clear it is not cooperating with the international community. According to an AP report based on diplomats and UN officials in Vienna, Iran has denied access to its underground nuclear sites to UN inspectors. This is the first time that Iran has refused to allow inspectors access to its nuclear facility in Natanz, where uranium is being enriched. Iran's refusal to allow such access could seriously hamper international attempts to ensure it is not trying to produce nuclear weapons as well as violate a key part of the Nonproliferation Treaty, diplomats and officials told AP. Outlining other signs of Iranian defiance, they said Iran denied entry visas to two IAEA inspectors in the last few weeks after doing so earlier this summer to Chris Charlier, the expert heading the agency's team to Teheran. Additionally, they said, other inspectors were only given single-entry visas during their visits to the country last week, instead of the customary multiple-entry ones. Informed sources in Washington on Monday said the most likely outcome from Iran's answer to the European offer would be an inconclusive response. Teheran is not expected to totally reject the package, but rather to accept parts of it and reject others, while not agreeing to the basic demand to immediately stop the uranium enrichment process. According to the sources, such a response would be crafted in a way that would be seen by some Security Council members - mainly Russia and China - as a partial compliance, while the US and Europe would interpret it as a rejection of the offer. This would force the US to reenter lengthy negotiations with the five permanent members of the Security Council before a decision to impose sanctions could be reached. US Undersecretary of State Nicholas Burns last week said the US had an agreement with the other permanent members of the Security Council, including Russia and China, that if Iran failed to comply with the UN decisions by August 31, there would be a need to impose international sanctions under Article 7 of the UN Charter. The US has not specified what the nature of the sanctions it seeks to impose would be, but made clear in discussions with its European counterparts that the sanctions will be directed at the regime in Teheran, not at the Iranian people. The Security Council has threatened sanctions if Iran remains defiant. Diplomats on Monday told AP these could include a ban on missile and nuclear technology to Teheran; international refusal to grant entry visas to those involved in Iran's nuclear program; and a freeze of their assets as well as a ban on investment in the country. IAEA head Mohamed ElBaradei is due to report by September 11 to the agency's board of governors on Iran's compliance and on other aspects of Teheran's cooperation with agency attempts to establish whether it has nuclear weapons aspirations. US Ambassador to the United Nations John Bolton said "nothing surprises me about how Iran treats its obligations" under the nuclear nonproliferation agreement. He told reporters Iran had concealed things from inspectors in the past and alleged that Teheran also had falsified data. Bolton said he had no specific knowledge of Iran's latest blocking of UN inspectors, but added: "More obstructionism doesn't surprise me at all." IAEA officials refused to comment. The Islamic republic has said it would formally respond by Tuesday to a six-power offer of economic and political rewards if it freezes enrichment and negotiates on its nuclear program. Iranian officials have said the country intended to move toward large-scale uranium enrichment involving 3,000 interconnected centrifuges in underground halls at Natanz, in central Iran, by late this year and would later expand the program to 54,000 centrifuges. Former UN nuclear inspector David Albright, president of the Washington-based Institute for Science and International Security, described the site as a vast complex 23 meters underground, covered by layers of materials. It is unclear whether that includes concrete. Despite optimistic forecasts by Iranian officials on the future of Natanz, Albright has said the Iranians have shown signs that they're having problems with the technology - a key hurdle. Albright's group has suggested that - if it were interested in producing bombs - Iran could create a basic small plant of 1,500 centrifuges, to make enough bomb fuel for one weapon. But the group has estimated that it would take three more years. For now, Iran's known enrichment capabilities consist of 164 centrifuges connected in series or a "cascade," at its surface pilot plant at Natanz. AP contributed to this report.