WASHINGTON (REUTERS) - The United States said on Thursday (Jan 4) it was suspending at least US$900 million (S$1.2 billion) in security assistance to Pakistan until it takes action against the Afghan Taleban and the Haqqani network militant groups.

The US State Department announced the decision, saying it reflected the Trump administration's frustration that Pakistan has not done more against the two groups, which have long used sanctuaries in Pakistan to launch attacks in neighbouring Afghanistan that have killed US, Afghan and other forces.

The department declined to say exactly how much aid would be suspended, saying the numbers were still being calculated and included funding from both the State and Defense departments.

US officials said two main categories of aid are affected: foreign military financing (FMF), which funds purchases of US military hardware, training and services, and coalition support funds (CSF), which reimburse Pakistan for counter-terrorism operations. They said they could make exceptions to fund critical US national security priorities. CSF funds, which fall under Defense Department authority, are covered by the freeze, said Pentagon spokesman Commander Patrick Evans, saying Congress authorised up to US$900 million in such money for Pakistan for fiscal year 2017, which ended on Sept 30. None of that money has yet been disbursed.

The freeze also covers US$255 million in FMF for fiscal year 2016, which falls under State Department authority and whose suspension has already been announced, as well as unspecified amounts of FMF that went unspent in earlier fiscal years.

Briefing reporters, US officials stressed the suspension did not affect civilian aid to Pakistan

and that the money could go through if Islamabad took decisive action against the groups.

"Our hope is that they will see this as a further indication of this administration's immense frustration with the trajectory of our relationship and that they need to be serious about taking the steps we have asked in order to put it on more solid footing," a senior State Department official told reporters.

"We're hoping that Pakistan will see this as an incentive, not a punishment," he added.

The Trump administration briefed Congress on its decision on Wednesday.

Pakistan has long rejected accusations that it fails to tackle the militants battling the Kabul government and foreign forces from sanctuaries on the Pakistani side of the border. It is largely shrugging off the proposed US aid cuts but frets that Washington could take more drastic measures to deter what it sees as Pakistan's support for the Taleban. Tense ties between the uneasy allies nosedived on Jan. 1 when U.S. President Donald Trump lashed out on Twitter against Islamabad's "lies and deceit" despite US$33 billion in
aid and the White House warned of "specific actions" to pressure Pakistan.

Trump's frustrations are shared by some U.S. lawmakers, who accused Pakistan of playing a double game by allowing militant groups sanctuary - which Islamabad denies - despite promising to crack down on them. "

Pakistan is one of the most duplicitous governments I've had any involvement with," Senator Bob Corker, Republican chairman of the Senate Foreign Relations Committee, told reporters. "Their, in essence, support of the Haqqani network, or ... allowing them to have safe harbor in their country when they're the greatest threat to our men and women in uniform."

South Asia expert Christine Fair of Georgetown University voiced concern that Pakistan might retaliate for the suspension by closing the highways from the port city of Karachi on which equipment is trucked to land-locked Afghanistan and the airspace through which supplies are flown to U.S.-led international forces there.

"What is the plan if they close the GLOCs?" she asked, using the military acronym for Ground Lines of Communications. "What if the Pakistanis shut down the ALOCs (Air Lines of Communications). How do you keep supplying the ANSF?" she asked, referring to the Afghan national security forces. "

Pakistan could be within their rights if they tell us you don't have flyover rights anymore," she said.