Four Palestinian armed groups on Sunday threatened to attack American targets in response to the US decision to veto a United Nations Security Council resolution condemning last week's tragic incident in Beit Hanun. The threat, the second of its kind in the past few days, was included in a statement issued by the Popular Resistance Committees, Fatah's Aksa Martyrs Brigades, Abu Rish Brigades [another Fatah militia] and a hitherto unknown group calling itself Brigades of Tawhid. The groups warned the Americans that "by supporting Israel's war crimes and massacres, you have turned yourselves into a legitimate target for all Palestinians and Muslims." They called on Muslims to deal "merciless blows" to the Americans wherever they are founded. "The American-Zionist enemy understands only the language of blood and force," the groups said. "This is the only way for us to achieve our rights and demands." The statement claimed that US Army officers participated in the last IDF military operation in Beit Hanun, which was aimed at halting the firing of Kassam rockets into Israel. Some Palestinian groups in the Gaza Strip issued a similar threat against the US shortly after the Beit Hanun incident, in which 19 civilians were killed. Palestinian threats to attack US targets have also been made in the past. However, the Palestinians never carried out the threats, with the exception of the kidnapping of a number of US citizens in the West Bank and Gaza Strip - all of whom were eventually released unharmed. Hamas Government Spokesman Ghazi Hamad condemned as "shameful" the US veto, saying it "gives Israel unlimited cover to commit more massacres of innocent Palestinians." Meanwhile, sources close to Hamas revealed on Sunday that the Islamic movement has nominated Muhammed Shabir, an academic from the Gaza Strip, to head the proposed unity government with Fatah. Prime Minister Ismail Haniyeh declared over the weekend his readiness to quit his job to pave the way for the formation of a unity government that will convince the international community to resume financial aid to the Palestinians. Representatives of Hamas and Fatah held intensive talks in Gaza City on Sunday in an attempt to reach a final agreement on the unity government, which will consist of Hamas and Fatah representatives, as well as a number of technocrats. The talks are being held under the auspices of Haniyeh and former PA Prime Minister Ahmed Qurei, who is a top Fatah leader. Born in 1946, Shabir has been described as a "prominent academic closely associated with Hamas," though he's never been a member of the movement. Her first studied pharmacy in Egypt, before moving on to study medicine in a West Virginia university. In the late 1970s he returned to the Gaza Strip, where he became a lecturer at the Islamic University and Dean of the Science Faculty. In 1993 he was appointed President of the Islamic University, a job he held until last August. His father, Sheikh Eid, was one of the leaders of the Muslim Brotherhood Organization in the Gaza Strip in the 1950s and 1960s.