Four believed to have been killed after up to 15 militants entered the Mehran naval station in the southern city of Karachi Islamist militants have stormed one of Pakistan’s largest military bases, attacking a US supplied surveillance aircraft, in a move that will cause further embarrassment for the country just weeks after the death of Osama bin Laden. Four people including a Pakistani navy officer and a fire fighter were believed to have been killed after up to 15 militants entered the high-security Mehran naval station in the southern city of Karachi. The attack late on Sunday is believed to be the most serious attack against the military since October 2009. According to navy spokesman Irfan ul Haq, the fighters split up into smaller groups to set off the explosions before hiding in the sprawling security facility. A P-3C Orion, a maritime surveillance aircraft recently given to Pakistan by America, was destroyed, a second navy spokesman, Salman Ali, said. One report said a team of US technicians were working on the aircraft at the time of the strike, but US Embassy spokesman Alberto Rodriguez said no Americans were on the base. The attack began with at least three loud explosions heard by people who live around the base, according to one report. while the Associated Press reported there were at least six other explosions and sporadic firing. Several dozen navy and police commandos sent in to battle the militants were met with gunfire and grenades from the militants, said Ali. The coordinated strike rocked Pakistan’s largest city just under three weeks after the death of terrorist leader Osama bin Laden in a US raid on the northwestern garrison city of Abbottabad. Extremists allied with al-Qaida have vowed to avenge his death. The killing of bin Laden triggered a strong backlash in the country against Washington, trying to support Pakistan in its fight against militants, as well as rare domestic criticism against the armed forces for failing to detect or prevent the operation. Pakistani Prime Minister Yousuf Raza Gilani condemned the attack, saying such a “cowardly act of terror could not deter the commitment of the government and people of Pakistan to fight terrorism.” Sunday’s raid appeared to be most serious against the military since October 2009, when militants attacked the army headquarters near the capital, Islamabad. The country’s security forces, following heavy US prodding, have launched several operations against militants in their heartland close to the border with Afghanistan over the last three years. But extremists have struck back against police and army targets around Pakistan. No group has claimed responsibility for the attack. However the Pakistani Taliban, an al-Qaida allied network which has previously launched attacks in Karachi, has pledged to retaliate for the death bin Laden, and has claimed responsibility for several bloody attacks since then. The US gave two Orions to the Pakistan navy at a ceremony at the base in June 2010 attended by 250 Pakistan and US officials, according to the US Central Command website. It said by late 2012 the Pakistan would have eight of the planes. Global terrorism Pakistan Amy Fallon guardian.co.uk