Scores of Hamas members were arrested in sweeps by Palestinian security throughout the West Bank overnight after the shooting of four Israelis on the eve of new Middle East peace talks.
The raids appeared to be a message from the government of Palestinian President Mahmoud Abbas to both its Hamas rivals and to Israel that it is committed to the talks. Hamas condemned the crackdown as "treason".
Israeli Prime Minister Benjamin Netanyahu said he would not let the shooting derail the negotiations.
Israel and the Palestinians are in Washington to begin talks aimed at creating an independent Palestinian state alongside Israel.
The talks are to focus on core issues of the conflict, including the status of east Jerusalem, which the Palestinians want as capital of their future state.
In a possible hint on the Israeli position on Jerusalem, Israeli Defence Minister Ehud Barak indicated that Israel would be willing to reach a compromise on the status of the city.
"West Jerusalem and 12 Jewish neighbourhoods that are home to 200,000 residents will be ours. The Arab neighbourhoods in which close to a quarter million Palestinians live will be theirs," Mr Barak said.
He said "a special regime" would be needed around the Old City - home to sensitive Jewish, Christian and Muslim holy sites.
The shootings yesterday immediately cast a shadow over President Barack Obama's push for Middle East peace, which formally began today with a White House dinner. It will be the first direct talks between Israeli and Palestinian leaders in nearly two years.
It also was a vivid reminder that while Hamas is locked out of the peace efforts, it remains a key player in determining the outcome of negotiations. The Iranian-backed group rules the Gaza Strip, one half of the territory claimed by the Palestinians for a future state, and has the power to sabotage negotiations at any moment.
During a visit to a West Bank army base Mr Barak said the military "will do everything possible to quickly bring the perpetrators to justice." But he urged residents to show restraint.
A Palestinian security official confirmed a crackdown was under way, but gave few details. He said the attackers from the shooting had not been found.
Mr Abbas, a Western-backed moderate, has carried out frequent crackdowns on Hamas since the Iranian-backed group defeated his forces and overtook Gaza three years ago. In turn, Hamas has frequently targeted members of Abbas' Fatah movement in Gaza.
Yesterday's attack occurred near Hebron, when a gunman opened fire on a passing vehicle, killing all four passengers inside - two men and two women from settlements in the area. The dead included a married couple with five children.
Today hundreds of mourners attended a funeral in Beit Haggai, a settlement near Hebron where two of the victims lived.
Hebron has been a frequent flashpoint of violence in the past. Around 500 ultra-nationalist Jewish settlers live in heavily fortified enclaves in the city, surrounded by more than 100,000 Palestinians.
Hamas, which refuses to recognise Israel's right to exist and has condemned the new peace talks, quickly took responsibility for the shooting and vowed that more attacks would follow. About 3,000 Palestinians joined a rally in Gaza to celebrate the attack.
The shooting occurred shortly before Mr Netanyahu landed in Washington, where he said that he would not let the violence disrupt the peace efforts. "We will not let terror decide where Israelis live or the configuration of our final borders," he said.