Hamas is threatening to avenge the assassination of Mahmoud al-Mabhouh – a veteran militant allegedly murdered by an Israeli intelligence hit-squad in Dubai.
Hamas says Mossad agents lured al-Mabhouh to a hotel room, immobilized him with an electric shock and suffocated him.
During an anti-Israeli rally in Jebaliya, north of Gaza city, Hamas leader Khaled Mashal addressed the crowd by video link from Damascus.
“I say this is enough. The time of promising and talking about revenge is over. Today is the time for action,” he said.
The assassination team is believed to have been up to 18 strong and included two women.
British Prime Minister Gordon Brown has ordered an investigation by the Serious Organised Crime Agency (Soca).
Israel’s ambassador to the UK has been called in to the Foreign Office to face questions over how the passports of six Britons living in Israel were used by members of the assassination squad to travel to Dubai.
UK detectives are flying out to the United Arab Emirates to liaise with the authorities there.
Israel’s Foreign Minister Avigdor Lieberman has not actually denied Israeli involvement but said: “There is no reason to think that it was the Israeli Mossad and not some other intelligence service or country up to some mischief.”