The radical Islamist group Fatah al-Islam, which was recently crushed by the Lebanese army, has begun operating inside the Gaza Strip, Palestinian Authority officials said Tuesday. In a statement issued in the Gaza Strip, the group claimed responsibility for the firing of homemade rockets at Sderot on two different occasions over the past few weeks. The Sunni Islamist group, whose name means "Conquest of Islam," was established in November 2006 and draws inspiration from al-Qaida. Earlier this year, the group engaged in fierce fighting with the Lebanese army in the Nahr el-Bared refugee camp in northern Lebanon. Dozens of Palestinians and Lebanese were killed in the clashes, which also resulted in the destruction of hundreds of homes in the camp. "Hamas is responsible for the presence of Fatah al-Islam in the Gaza Strip," said Ahmed Abdel Rahman, a top aide to PA President Mahmoud Abbas. "This is an extremely dangerous development because Fatah al-Islam, which is not linked to Fatah, is a radical terrorist organization." Abdel Rahman said the state of anarchy and lawlessness created by Hamas's violent takeover of the Gaza Strip six months ago was the main reason behind the emergence of such radical groups there. "The Hamas government and its illegal militias are fully responsible for the infiltration of Fatah al-Islam into the Gaza Strip," he added. "The presence of this dangerous gang of mercenaries in the Gaza Strip will bring more tragedies and disasters to the Palestinians." Abdel Rahman said that the presence of the group in the Gaza Strip also provided Israel with an "excuse to continue its incursions and assassinations." If the claim is true, Fatah al-Islam joins a long list of radical Islamist groups that have popped up in the Gaza Strip in recent years. They include Hizb al-Tahrir (Party of Liberation), Fatah al-Yasser, Qaida al-Islam, Army of Islam, Suyuf al-Haq (Swords of Justice) and the Nasser Eddin Brigades. In another development, Hamas said Tuesday that it would not allow Fatah-controlled security forces to take over the Rafah border crossing without its permission. The announcement came in response to statements made by PA officials in Ramallah to the effect that they were discussing the possibility of reaching an agreement with Egypt over control of the Rafah terminal, which has been closed since Hamas took full control over the Gaza Strip. Muhammad Madhoun, director of the office of Hamas Prime Minister Ismail Haniyeh, said that while Hamas was not opposed to the border's reopening, it insisted that the move be carried out in coordination with the Islamist movement. Madhoun pointed out that Hamas had previously suggested handing control of Rafah to a private company, but the PA and the Egyptians had turned down the offer. Meanwhile, Fatah has decided to cancel celebrations in the Gaza Strip marking its 43rd anniversary after receiving threats from Hamas, Fatah activists said. They said a major rally scheduled to take place on January 1 in Gaza City had been called off after Hamas threatened to arrest the organizers. Earlier this month, Fatah's security forces prevented Hamas from celebrating its 20th anniversary in the West Bank. The move prompted Hamas leaders to call for a similar ban on Fatah celebrations in the Gaza Strip.