The US announced a $2bn (£1.3bn) arms sales deal with Pakistan today to help boost the fight against Taliban and al-Qaida groups using the country as a safe haven for attacks inside Afghanistan.

The deal, to be spread out over the next five years, amounts to about a 30% increase in US funding for weapons sales to Pakistan.

US-Pakistan relations are turbulent, constantly switching between Washington criticising Pakistan for a lack of commitment to fighting extremism to insisting it is one of its most important allies.

The planned increase in spending was announced by the US secretary of state, Hillary Clinton, at the end of a three-day US-Pakistan summit in Washington attended by senior military, diplomatic and political representatives of both countries.

Clinton sought to appease the Pakistani government and public opinion bruised by recent criticism from the US. "I want to say publicly what many of us have said privately: the United States has no stronger partner when it comes to counter-terrorism efforts against the extremists who threaten us both than Pakistan," she said.

The Pakistani foreign minister, Shah Mehmood Qureshi, standing beside Clinton, said: "There are still tongue-in-cheek comments, even in this capital, about Pakistan's heart not really being in this fight," he said. "We do not know what greater evidence to offer than the blood of our people. Madam secretary, we are determined to win this fight."

US congressional approval is likely to be forthcoming, but sceptical members will raise awkward questions, especially after reports last year that earlier military aid to Pakistan had gone missing or was diverted from counter-terrorism to bolstering defences against India.

Congress has also expressed concerns about human rights abuses by the Pakistani military, in particular over its offensive in the Swat valley last year. Under US law, the Obama administration is planning to withhold military aid going to any units involved in alleged human rights abuses.

"If there is going to be progress against al-Qaida, we need the support of the Pakistani army," the Democratic senator, Patrick Leahy, said earlier.

"But there is a lot of concern with extrajudicial killings by the army that remain unpunished, and this will be a factor when we consider a request for more aid. Respect for our law and the laws of war is fundamental."

The military aid comes on top of $7.5bn in civilian assistance already promised for the next five years.

The US hopes that Pakistani military offensives against Taliban and al-Qaida bases along the Afghanistan border will help reduce violence in Afghanistan. But the aid is also aimed at stabilising Pakistan at a time when Washington is fearful of the country, and its nuclear weapons, falling into the hands of Islamist extremists.