Israel and the Palestinian Authority (PA) have differed sharply over the killing of a Hamas commander in the West Bank city of Hebron.
Israel imposed a curfew in Hebron after the shooting
Israeli Prime Minister Ariel Sharon hailed his troops for their "successful and highly important operation" and promised more such attacks if the PA did not tackle militant groups itself.
But Palestinian officials accused Israel of seeking to prevent them securing a ceasefire deal. Hamas itself vowed revenge but said it would continue to consider a truce.
In Jordan, US Secretary of State Colin Powell said the shooting of the Hamas commander was a "matter of concern" and expressed "regret" that "once again we had an incident that could be an impediment to progress".
These operations are meant to obstruct any success of the dialogue to reach a truce
Yasser Abed Rabbo
The BBC's Paul Wood, in Jordan, says that in the rarefied world of international diplomacy, that counts as a severe dressing-down for Israel.
The Americans are clearly furious that once again the effort to get a ceasefire agreement from Palestinian militants has been set back by Israeli military action, our correspondent adds.
In an incident a day after the killing of the Hamas commander, four Palestinians were killed in the West Bank town of Beit Hanoun, Palestinian medical sources said.
Palestinian sources said the four had been killed by Israeli tank fire, but the army denied that.
An army statement said they had most likely been killed by the premature explosion of a bomb they were planting, and said there had been no firing in the area at the time.
Blamed for bombings
Israel held the Hamas commander, Abdullah Qawasmeh, responsible for three suicide bombings this spring including the Jerusalem attack which killed 17 people on
He was shot dead by an elite Israeli army unit on Saturday night in disputed circumstances.
"This was a vital action designed to provide security for Israel's citizens," said Mr Sharon.
Israel sees Hamas as the biggest threat to its security
If the Palestinians did not take serious action against "terrorism", he added, Israel would continue to carry out such operations.
Palestinian cabinet minister Yasser Abed Rabbo said the killing of the Hamas commander was meant to "obstruct any success of the dialogue to reach a truce".
Main Erekat, the spokesman for Palestinian Prime Minister Mahmoud Abbas (Abu Mazen), stressed to the BBC that Mr Abbas was engaged in intensive negotiations with Palestinian factions to try to end the violence.
If Israel persisted with such actions, progress would be impossible, he told the Newshour programme.
The Israelis say their forces tried to arrest Qawasmeh and only opened fire after he pulled a gun.
But Palestinian sources said Mr Qawasmeh was shot while standing at the entrance to a mosque.
Hamas leader Abdel-Aziz al-Rantissi - who survived an Israeli attempt to kill him earlier this month - said the killing in Hebron would "not go unpunished".
The attack clearly showed that Israel would "continue to shed Palestinian blood", he said.
Mr Powell described Hamas as an "enemy to peace" on Friday and urged Mr Abbas not to wait for it to agree a truce before starting to implement the roadmap.
Mr Powell said the peace process must continue
Speaking in Jordan on Sunday after meeting the other members of the Middle East peace quartet who drafted the roadmap - the European Union, Russia and United Nations - Mr Powell said the peace process must keep going forward whatever "incidents" might occur.
United Nations Secretary General Kofi Annan, who was also in Jordan for the Wold Economic Forum, referred to a process of "parallelism".
He called on Israel to refrain from military activity in civilian areas, demolishing Palestinian homes and engaging in "extrajudicial killings".