Ties between the United States and Pakistan have veered between extremes over the past four decades. Here are some of the key moments in their turbulent relationship:

1980s: United States pumps weapons, money and foreign fighters into Afghanistan, with the help of Pakistan’s Inter-Services Intelligence (ISI) spy agency, to support mujahideen fighters defeat Soviet Union troops in Afghanistan.

1990: The United States imposes sanctions on Pakistan over Islamabad’s covert nuclear programme. With the Soviet Union routed in Afghanistan and the Cold War ending, Pakistan had lost its importance as a regional ally.

1998: The United States imposes sanctions on Pakistan and India over their nuclear tests.

1999: Washington imposes more sanctions on Pakistan after army chief Pervez Musharraf topples a democratically elected government in a military coup.

2001: After the Sept 11 attacks on New York and Washington, the United States asks Musharraf to help track down al Qaeda and remove the Taliban from power.

* Washington removes all sanctions against Pakistan in the wake of Pakistan’s support for its war against al Qaeda and other Islamist militant groups in Afghanistan.

2004: George W Bush’s administration designates Pakistan a “major non-NATO ally”, boosting Islamabad’s diplomatic prestige and giving Pakistan greater access to US military technology.

2011: CIA contractor Raymond Davis kills two Pakistanis in the eastern city of Lahore in January 2011. Davis was acquitted of murder and allowed to leave Pakistan after a $2.3 million payment was made to the men’s families.

* US troops kill Osama bin Laden on Pakistani soil in May 2011in a raid that was kept secret from Pakistani authorities.

* NATO helicopters and fighter jets attack Pakistani military outposts by accident, killing 24 soldiers. Pakistani retaliated by blocking a NATO supply route through its territory to Afghanistan for more than seven months.

2016: US Congress blocks the sale of F-16 fighter jets to Pakistan. Military aid to Pakistan reduced.

2017: US President Donald Trump outlines a new South Asia policy. Trump accuses Pakistan of harbouring “agents of chaos” and providing safe havens to militant groups waging an insurgency against the US-backed government in Kabul.