A US drone strike targeting a vehicle killed at least three militants on Monday in a restive Pakistani tribal region near the Afghan border, security officials said. The strike took place in the Khaider Khel area of Mir Ali district, 30 kilometres (18 miles) east of Miranshah, the capital of North Waziristan tribal region, known as a stronghold of Taliban and Al-Qaeda militants. "US drones fired four missiles on a militant vehicle, killing three rebels," a security official told AFP, adding that several drones were flying in the area at the time of the attack. Another security official confirmed the attack and casualties and said the identities of the militants killed in the strike were not immediately clear. The Al-Qaeda-linked Haqqani network in North Waziristan, blamed for some of the deadliest attacks in Afghanistan, is one of the thorniest issues between Islamabad and Washington. Washington has long demanded that Pakistan take action against the Haqqanis, whom the United States accused of attacking the US embassy in Kabul in September last year and acting like the "veritable arm" of Pakistani intelligence. Pakistan has in turn demanded that Afghan and US forces do more to stop Pakistani Taliban crossing the border from Afghanistan to launch attacks on its forces. There has been a dramatic increase in US drone strikes in Pakistan since May, when a NATO summit in Chicago failed to strike a deal to end a six-month blockade on convoys transporting supplies to coalition forces in Afghanistan. Islamabad and Washington have been seeking to patch up their fractious relationship in recent months, with the supply route has reopening, after a series of crises in 2011 saw ties between the "war on terror" allies plunge. But attacks by unmanned US aircraft remain contentious -- they are deeply unpopular in Pakistan, which says they violate its sovereignty and fan anti-US sentiment, but American officials are said to believe they are too important to give up. Washington considers Pakistan's semi-autonomous northwestern tribal belt as the main hub of Taliban and Al-Qaeda militants plotting attacks on the West and in Afghanistan.