Amid numerous calls for the construction of an effective border fence between Egypt and Israel, senior government officials said Monday it was not clear that the suicide bombers who attacked Dimona in the morning had come across the border from Egypt. The officials said the defense establishment was investigating where the attackers originated, and with what organization they were affiliated, and was "not jumping to any conclusions." Senior diplomatic officials said they were unaware of any messages that had been passed on to Cairo regarding the attack. Prime Minister Ehud Olmert pledged that Israel "will not relent" in its struggle against terrorists. Addressing the Knesset, Olmert said that Israel is facing a "constant war" in the southern part of the country. Referring to the Dimona attack, Olmert said: "It was a very harsh incident that only points again to the complexity that we deal with daily. I have said more than once in the past few weeks that a constant war is being conducted in the south of the country, a war of terror against us and our war against terror, this war will continue, terrorism will be hit. We will not relent." Speaking earlier at a Kadima faction meeting in the Knesset, the prime minister said the attack "gives us a painful reminder that we must be vigilant and maintain our readiness in all areas." Olmert, who told faction members that the IDF had killed one of the leaders of the Popular Resistance Committees in Gaza shortly after the Dimona attack, said "a war is being waged between us and the terrorists, and it is continuing without let-up. We will reach everyone who is involved in terrorism, dispatches terrorists, and tries to harm Israeli citizens." Olmert added that Israel had had a number of successes in this sphere in recent weeks and days that could not be made public. Senior ministers, from Defense Minister Ehud Barak, to Foreign Minister Tzipi Livni and Transportation Minister Shaul Mofaz, repeated calls heard in Sunday's cabinet meeting for the rapid construction of a fence on the Egyptian border. Government officials said that since it was clear Israel would not pursue terrorists across the border into Egypt, what needed to be developed were state-of-the-art defenses on the border that would ensure that the terrorists could not get in. The calls to construct a fence came amid fears that terrorists from the Gaza Strip have crossed into Egypt through the breach in the Gaza border and could easily penetrate into Israel from Sinai. Despite calls from Industry, Trade and Labor Minister Eli Yishai to halt negotiations with the Palestinian Authority because of Monday's attack, it was clear that this was not Israel's policy. Livni has said on numerous occasions that both Israel and the Palestinians must continue with peace talks despite actions on the ground that may lead to calls in either camp to halt them. Yishai also said Israel should consider re-taking control of the Philadelphi Corridor along the Egypt-Gaza border. "The previous government's decision to abandon the Philadelphi Corridor without supervision was a bad mistake," Yishai said. President Shimon Peres, meanwhile, issued a statement saying the attack was carried out by "loathsome individuals who wanted to murder innocent women and children as well as kill any chance of peace and quiet in the region." The attack was widely condemned around the world. UN Special Envoy to the Middle East Robert Serry expressed sympathy with the residents of Dimona and pointed out that he had been in Sderot two weeks ago when the came under a barrage of rockets from Gaza. "These terrorist actions of course serve no legitimate purpose," he said. "The UN condemns terror. Nothing can justify such attacks." Slovenia, which currently holds the rotating presidency of the EU, issued a statement condemning the attack "in the strongest terms." "This act of terror, for which there can be no justification, was aimed at innocent civilians with the goal of undermining the peace process," the statement read. "The Presidency therefore encourages Israel and the Palestinian Authority to pursue with determination the political process agreed in Annapolis." And Quartet envoy Tony Blair, scheduled to arrive in Israel on Tuesday for a round of talks, issued a statement saying the attack "shows the security concerns of Israel remain real, and [shows] the absolute necessity of isolating and defeating the extremists who want hate and terror in place of peace and reconciliation." According to a spokeswoman for Blair, the Quartet envoy - scheduled to remain in the region until Friday - will continue pursuing economic projects and capability-building projects with the Palestinians. In an interview that appeared Saturday in The Times, Blair said, "The question is how do you create the circumstances on the ground where the Israelis get confidence that their security concerns are being met and the Palestinians get confidence that the occupation will eventually be lifted." According to Blair, "Without that confidence about the state of the situation on the ground the negotiation becomes more difficult. Sometimes people have looked at this process as one in which if you cut the deal the facts on the ground will alter. In my view, it is as much the other way around. Unless you can change the facts on the ground the deal becomes difficult to cut." Blair is scheduled to arrive a day after another top-flight envoy, the US's James Jones, leaves the country for Amman after four days of talks with Israeli and Palestinian officials. Jones, the US Special Envoy for Middle East Security, is currently at work drawing up a plan on how to provide security in the interim period between when Israel leaves large swaths of the West Bank under any possible peace agreement, and when the PA is able to take over control of the vacated areas. Jones spent the morning with IDF officials in the South, and met Barak before heading off to Amman in the evening.