WASHINGTON - Opening Mideast talks just after fresh violence, President Barack Obama on Wednesday warned militant Hamas that the United States and its allies won't be stopped in their pursuit of peace by the acts of terrorists. Standing with Israeli Prime Minister Benjamin Netanyahu at the White House, Obama condemned the killings on Tuesday of four Israelis who were shot while traveling near the West Bank city of Hebron. Hamas, which rejects Israel's right to exist and opposes peace talks, claimed responsibility. "I want everybody to be very clear," Obama said. "The United States is going to be unwavering in its support of Israel's security. And we are going to push back against these kinds of terrorist attacks. And so the message should go out to Hamas and everyone else who is taking credit for these heinous crimes that this is not going to stop us." Netanyahu praised Obama for his support and for expressing the sentiments of "decent people everywhere." Both leaders said their opening talks on Wednesday morning, part of a series of separate discussions, that also were to include Palestinian President Mahmoud Abbas, were productive. President Barack Obama opened a new round of Mideast peacemaking Wednesday, bringing Israeli and Palestinian leaders to the White House for talks aimed at forging agreement within one year on a two-state solution: a sovereign Palestine and a secure Israel. Obama met first with Israeli Prime Minister Benjamin Netanyahu, and later he was meeting with Palestinian President Mahmoud Abbas. After separate sessions with the leaders of Jordan and Egypt, the five men were to gather for dinner. Formal negotiations between the Israeli and Palestinian leaders are to begin Thursday at the State Department, with Secretary of State Hillary Rodham Clinton serving as host. Clinton has spent months coaxing the parties back to the bargaining table. It will mark the first face-to-face negotiations between the Israelis and Palestinians since December 2008, but the two sides are far apart on all key issues, so major progress in the early going is seen as unlikely. Pointing up the tensions that will probably test Obama's diplomacy, a Palestinian gunman opened fire Tuesday on an Israeli vehicle traveling near the West Bank city of Hebron, killing four passengers. The militant Hamas movement, which rejects Israel's right to exist and opposes peace talks, claimed responsibility. Israeli officials called the shooting an attempt to sabotage the discussions and the White House weighed in with its own condemnation. "This brutal attack underscores how far the enemies of peace will go to try to block progress" in the talks, White House press secretary Robert Gibbs said in a strongly worded statement. "It is crucial that the parties persevere, keep moving forward even through difficult times, and continue working to achieve a just and lasting peace in the region that provides security for all peoples." In remarks to reporters before their meeting Tuesday evening at a Washington hotel, Netanyahu, with Clinton at his side, said: "We will not let terror decide where Israelis live or the configuration of our final borders. These and other issues will be determined in negotiations for peace that we are conducting and in these negotiations." Clinton was equally firm. "We pledge to do all we can always to protect and defend the state of Israel and to provide security to the Israeli people," she said. "That is one of the paramount objectives that Israel has and the United States supports in these negotiations." West Bank settlers said Wednesday they will break a government freeze on construction in their communities to protest the attack. On Wednesday, Abbas and Netanyahu were to meet separately with Obama. Then, joined by Jordan's King Abdullah and Egyptian President Hosni Mubarak, they will attend a White House dinner intended to set the stage for the launch of formal talks a day later at the State Department. Jordan and Egypt are the only two Arab nations with peace deals with Israel.