The image of Palestinian leader Mahmoud Abbas and Israeli Prime Minister Ariel Sharon shaking hands across an ornate table at the Egyptian resort town of Sharm el-Sheik on Tuesday was a welcome sign of amity after four years of hostilities. Already, observers are proclaiming the informal truce reached by Israel and Palestine as the best opportunity for peace in years.

Those hopes are understandable, but they shouldn’t lull the world into believing the Sharm el-Sheik summit has set Sharon and Abbas on an exorable course toward peace. Turning an informal truce into a final settlement will not happen without the international community on sustained pressure on both parties.

As if to underscore the challenges ahead, the Palestinian militant group Hamas immediately said it would not be bound by the truce. That kind of tough talk is a sign the underlying dynamics fueling this conflict remain firmly in place. Groups such as Hamas and Islamic Jihad largely retain their ability to sink the peace process with well-timed attacks. The prospect of a renewed Israeli military offensive, such as the new security barrier and ever-expanding Jewish settlements in the West Bank, could be just as destructive to peace efforts.

Despite these stumbling blocks, there are signs subtle changes are underfoot. The death of Yassir Arafat in November removed a figure that Israel and the United States believed would always stand in the way of a peace agreement. His successor, Abbas, has openly questioned the wisdom of violent resistance and called for an end to Palestinian suicide attacks. Likewise, Sharon’s resolve to withdraw from the Gaza Strip in the face of intense political opposition is a clear admission the occupied territories are doing Israel more harm than good.

These are openings the United States, European Union, and Middle East powers such as Egypt and Jordan should exploit. A combination of diplomatic pressure and financial aid would give Abbas the will and the way to crack down on militants and solidify his political standing. U.S. diplomacy should take aim at curbing Israel’s habit of expanding its settlements and responding to suicide attacks with excessive force. Those moves would go a long way toward moving Israelis and Palestinians even further back from the brink.