At least 12 officials are reported to have been killed and 14 others injured in an ongoing attack by armed men on a military base in the Pakistani city of Karachi, according to Al Jazeera's sources. Some of the attackers are still inside the base and commandos and marines are continuing to battle them several hours after the assault began, Al Jazeera's Kamal Hyder said on Monday. Irfan ul Haq, Pakistan navy spokesman, said that 11 navy officers and one paramilitary ranger have been killed. Ongoing operation A spokesman for the Pakistani Taliban said that the team of militants they sent into Karachi's PNS Mehran naval base on Sunday night had enough supplies to survive a three-day siege. "They have enough ammunition and food and they can fight and survive for three days," Ehsanullah Ehsan, a Taliban spokesman, told Reuters news agency. Speaking to Al Jazeera, Fazal Qureshi, chief editor at the Pakistan Press International news agency in Karachi said: "This operation is probably one of the longest operations which we have seen in Pakistan. But now in the last one hour or so we have been told that it will end shortly, it is probably in its final stages." "These people are confined in one particular room, the commandos are advancing so whatever they have they will not be able to use the supplies." Qureshi added. "They have surrounded and confined the terrorists in one building, some four or five of the terrorists have been already killed." According to navy officials operation has been going on for hours because they are trying to capture the fighters alive. Aaamir Latif, bureau chief, online news network, told Al Jazeera that "Earlier there were reports that the militants had taken hostages but navy sources have said that is not the case." Taliban claim Intelligence officials said that between 15 and 20 attackers were inside the base, and had attacked three hangars housing aircraft. A military spokesman said two Pakistan Navy staff were killed in the attack. "One of our officers and one Navy personnel have been martyred," Commodore Irfan ul Haq, a spokesman for the Pakistan Navy, told the AFP news agency. Five explosions were heard at the base ahead of the attack, according to Pakistani Express TV. Yusuf Raza Gilani, Pakistan's prime minister, condemned the attack. "Such a cowardly act of terror could not deter the commitment of the government and people of Pakistan to fight terrorism," Gilani said in statement. Pakistani Taliban claimed responsibility for the attack and threatened further attacks. "It was the revenge of martyrdom of Osama bin Laden. It was the proof that we are still united and powerful," Ehsan of Taliban told agencies by telephone from an undisclosed location on Monday. "We had already warned after Osama's martyrdom that we will carry out even bigger attacks," he said, referring to previous vows to avenge the killing of the al-Qaeda leader by US special forces three weeks ago.