Palestinian militants today warned of swift and bloody retaliation against Israel after it "opened the gates of hell" by assassinating Ahmed Yassin, the founder and spiritual leader of militant group Hamas.
In scenes repeated in towns across the occupied territories, angry crowds called for revenge against Israel and the US, and masked militants fired automatic rounds into the air.
Violent clashes between demonstrators and Israeli security forces broke out and at least four Palestinians - including a 13-year-old boy and a journalist - were reported to have been killed when Israeli soldiers fired on the crowds.
"Words cannot describe the emotion of anger and hate inside our hearts," said Hamas official Ismail Haniyeh, who was a close associate of Yassin.
Abu Abeer, spokesman for a group of militant Palestinian organisations in the occupied territories, told pan-Arab satellite channel al-Arabiya there would be "swift and serious" repercussions.
"They have opened the gates of hell," he warned. "For us, everything is now permissible after this assassination."
For the first time, Hamas threatened revenge on the US as well as Israel, saying that US backing of Israel had made Yassin's assassination possible. The White House denied any involvement in the operation.
"All the Muslims of the world will be honoured to join in on the retaliation for this crime," Hamas said in a statement.
Within hours of the assassination, large protests erupted in Lebanon, Yemen and Egypt, where students flooded on to the streets of the capital Cairo and burned US and British flags.
But in Kuwait - one of the US's closest allies in the Arab world - the prime minister, Sheik Sabah al-Ahmed al-Sabah, warned: "Violence will increase now, because violence always breeds violence."
In a first response, Palestinian militants fired 10 home-made rockets toward an Israeli settlement in Gaza.