Palestinian suicide bombers have struck in Israel and the West Bank for the first time in over a month, killing two Israelis.
The attacks came within an hour of each other
One blast ripped through a shopping centre in the Tel Aviv suburb of Rosh Haayin and a bomber blew himself up at a bus stop outside the Jewish settlement of Ariel.
Two Palestinian militant groups claimed they carried out the attacks in specific retaliation for a deadly Israeli raid last week.
But officials from one group, Hamas, stressed that they were still keeping to their ceasefire.
Israel has called for a "complete halt to terror" and suspended its release of Palestinian prisoners, but a senior Israeli official suggested the releases would resume.
Israel had been expected to free 76 detainees on Tuesday before the attacks.
Zalman Shoval, a senior foreign policy adviser to Prime Minister Ariel Sharon, commented that "from the point of view of public opinion, today would not be a very suitable day to release Palestinian prisoners".
"But ultimately the Israeli Government is committed to releasing prisoners and I think it will continue to do that," he added.
Mr Sharon himself said there could be no progress on the US-backed roadmap to peace without a complete halt to attacks.
An Israeli military source quoted by AP news agency said there would be no large-scale retaliation for Tuesday's attacks.
The BBC's Simon Wilson in Jerusalem says the attacks are undoubtedly the severest threat yet to the period of relative calm since the main Palestinian militant groups announced a unilateral ceasefire in June.
In Rosh Haayin, the suspect bomber detonated a charge he was carrying - possibly in a backpack or in a belt - after being challenged by a security guard at the entrance to a supermarket.
Palestinian groups declared a unilateral truce on 29 June
An Islamic Jihad suicide bomber killed a woman in an Israeli village on 7 July
An Israeli raid on Nablus on 8 August left four Palestinians and one soldier dead
The blast left a mass of twisted blinds and shattered glass and sparked a large fire.
Firefighters with breathing equipment rushed to the scene to pull out the injured, some 10 people.
"I saw fire and a cloud of smoke," said witness Avigail Josef. "They brought out an injured child and then his mother."
The Palestinian militant group al-Aqsa Martyrs Brigade - part of Yasser Arafat's Fatah faction - claimed responsibility for the attack, saying it was to avenge an Israeli raid on Friday.
Two Hamas militants and two Palestinian civilians died in that raid which also claimed the life of one Israeli soldier.
In the Ariel attack, the bomber detonated his device at a bus stop near several young Israelis. He killed one and wounded three.
Hamas's armed wing claimed responsibility for the attack on its website.
Palestinian Prime Minister Mahmoud Abbas condemned both bombings but said they had been provoked by Israeli raids into Palestinian areas.
Militant groups, he added, were still committed to their truce with Israel.
A senior Palestinian legislator, Saeb Erekat, rejected Israeli suggestions that the Palestinian Authority could have acted to prevent the attacks.
Hamas's armed wing, al-Qassam Brigades, said in a statement that the Ariel attack was a response to the killing of its members in Nablus.
A senior Hamas leader, Abdel-Aziz al-Rantissi, said the killing of Palestinians would not be tolerated and he blamed Ariel Sharon for the new violence.
"For 40 days we have been committed to our imitative but Sharon has refused to accept that initiative and he has continued to kill," the Hamas official said.