The Bush administration faced Congressional criticism yesterday for diverting funds from Pakistan's faltering fight against the Taliban and al-Qaida to pay instead for upgrades of its US-built F-16 combat planes.

With increased fighting in Afghanistan, much originating with forces based in Pakistan's north-west, members of Congress questioned how the switch to the planes, intended mainly as a counter to the Indian air force, would contribute to quelling the insurgency.

The White House spokeswoman, Dana Perino, yesterday insisted: "The F-16s are used in counter-terrorism operations. We made them available to the Pakistanis, and they need to be maintained."

There is no record of the F-16s being much used in the tribal areas, mainly because Pakistan fears civilian deaths would increase hostility to its forces.

Nita Lowey, the Democrat who heads the House state and foreign operations committee, said: "Congress provided these funds specifically for counter-terrorism and law enforcement. It is incumbent on the state department and Pakistan to demonstrate clearly how these F-16s would be used to fight al-Qaida and the Taliban in order to get congressional support."

Almost $230m (£115m) in aid earmarked for counter-terrorism has been shifted to modernise the F-16s, built by Lockheed Martin, out of a total $300m budget the US gives Pakistan for military purposes.

The move puts George Bush at odds with Congress, which last year passed legislation specifying the money be used for counter-terrorism or law-enforcement.

Both the Pentagon and Democratic members of Congress, as well as the Democratic presidential hopeful Barack Obama, would like to see Pakistan's new government pursue a more aggressive strategy along the border, and argue fighting on the ground, supported by good intelligence, is more effective than air attacks. Democrats have hinted that, if Pakistan does not act, US forces will cross from Afghanistan.

The switch comes ahead of a visit by Pakistan's prime minister, Yousaf Raza Gilani, to Washington next week. President Bush phoned India's prime minister, Manmohan Singh, from his ranch in Crawford, Texas, to explain the decision, Perino said. Singh expressed disappointment, an Indian government spokesman said.

Speculation in Washington varied on the White House's motive, ranging from an incentive for Pakistan to pursue insurgents, to helping Lockheed.

A state department official said the timing was dictated by a need to pay Lockheed by the end of July. "This shift comes about as a result of a request from the Pakistan government, partly because of their cash-flow problems and partly because they are re-evaluating the equipment they need to fight the war on terror. Nato forces use F-16s right across the border ... in Afghanistan for similar purposes; and frankly, Pakistan has already used its F-16s in sorties against terrorist targets," an official said. "So it's a legitimate use, and it supports a democratic government."