DERA ISMAIL KHAN, Pakistan -- A suspected US drone killed at least six militants in northwestern Pakistan on Wednesday when it fired a missile at a house linked to a group that often carries out attacks on NATO troops in neighboring Afghanistan, intelligence officials said. The US has stepped up drone strikes in recent days, carrying out five suspected attacks in less than a week in North Waziristan, a tribal area along the border that is effectively controlled by militants at war with foreign troops in Afghanistan. The US refuses to publicly acknowledge such strikes, but officials have said privately that they have killed several senior Taliban and al-Qaida militants. Wednesday's strike hit a house in the village of Dande Darpa Khel near Miran Shah, the main town in North Waziristan, two Pakistani intelligence officials said on condition of anonymity because they were not authorized to talk to the media. The house was owned by Maulvi Azizullah, a member of the Haqqani network, a militant group based in North Waziristan that U.S. military officials have called the most dangerous threat to NATO troops in Afghanistan. The Haqqani network is closely allied with the Taliban and is led by Jalaluddin Haqqani, a well-known fighter during the war against the Soviets in Afghanistan. Haqqani received support from the US and Pakistan during the Soviet war but has since turned against the Americans. The US has repeatedly urged Pakistan to launch an offensive against the network, but the government has not done so, a decision many analysts believe is driven by Pakistan's desire to maintain its historical ties with the group. The militants have refrained from launching attacks inside Pakistan, and analysts believe the government views them as an important ally once foreign troops withdraw from Afghanistan. Without a Pakistani military offensive, the US has had to rely on drone strikes to battle the group. The Pakistani government has publicly criticized the missiles strikes as violations of its sovereignty, but many analysts suspect it actually helps the CIA carry out the attacks, especially when they target militants at war with Pakistan.