WASHINGTON - Pakistans security forces were not part of Sundays operation to kill Osama bin Laden, President Asif Ali Zardari has said, while also denying that al-Qaeda leaders killing in his country is a sign of its failure to combat terrorism. In an opinion piece, published in the Washington Post on Tuesday with the above headline, Zardari said that the deadly assault on the compound in Abbottabad holding bin Laden was not a joint operation between the United States and Pakistan. Nevertheless, Zardari stressed that the killing of bin Laden, the leader of Al Qaeda, was a result of years of cooperation between the United States and Pakistan. Zardari said the whereabouts of the al Qaeda leader, killed in a town some two hours north of Islamabad, were not known to the Pakistani authorities. Its inconceivable that bin Laden did not have a support system in the country that allowed him to remain there for an extended period of time, John Brennan, President Obamas top counterterrorism official, said at a White House briefing on Monday, as reported in the New York Times. There were disagreements among US officials Monday over how much the Pakistanis knew concerning bin Ladens whereabouts. Some said there was no indication Pakistanis knew bin Laden was at the Abbottabad compound. Others expressed deep scepticism, noting the proximity of bin Ladens compound to military academy. Zardari used his article to stress that Pakistan welcomes the killing of bin Laden and has been deeply affected by terrorist activity on its soil. He writes that he has been personally affected by terrorism, mentioning the assassination of his wife, Benazir Bhutto. And for me, justice against bin Laden was not just political; it was also personal, as the terrorists murdered our greatest leader, the mother of my children, Zardari wrote. Zardari also discussed Pakistans political situation, saying a freely elected democratic government, with the support and mandate of the people, working with democracies all over the world, is determined to build a viable, economic prosperous Pakistan that is a model to the entire Islamic world on what can be accomplished in giving hope to our people and opportunity to our children. We can become everything that al-Qaeda and the Taliban most fear a vision of a modern Islamic future. Our people, our government, our military, our intelligence agencies are very much united. Some abroad insist that this is not the case, but they are wrong. Pakistanis are united.