The United States added bite to its increasingly public spat with Pakistan over militant safe havens Thursday, suspending hundreds of millions of dollars in security assistance.
President Donald Trump's administration has expressed deep frustration at its South Asian ally's failure to crack down on the Afghan Taliban and Haqqani group bases.
Pakistan has pushed back strongly at Trump's intemperate language, raising concerns that to row could undermine Islamabad's support for US operations in Afghanistan.
But on Thursday, the State Department announced a dramatic freeze in deliveries of military equipment and security funding until Pakistan cracks down on the militants.
Officials confirmed that in September last year State had already suspended $255 million in funding to help Pakistan buy high-tech weaponry from US manufacturers.
- 'Decisive action' -
Now, the Defense Department has been instructed to stop making payments from "coalition support funds" set aside to refund Pakistani spending on counter-terrorist operations.
Exemptions will be made in cases of "critical national security" and officials refused to put a figure on how much Pakistan will lose out on if it fails to cooperate.
But the National Defense Authorization Act permits the US military to spend up to $900 million in the 2017 financial year and $700 million in financial 2018.
State Department spokeswoman Heather Nauert said the security spending would be suspended until Pakistan takes "decisive action" against the Afghan Taliban and Haqqani network.
Pakistan has fought fierce campaigns against some Pakistani militant Islamist groups that threatened its own security.
But US officials accuse Pakistani officials of ignoring or even collaborating with groups that launch operations into Afghanistan from safe havens along the countries' border.
These groups threaten the US-backed Afghan government and have attacked and killed many of the American troops that were sent there after the September 11, 2001 attacks.
US frustration has boiled over before.
Trump's predecessor Barack Obama authorized drone strikes on Pakistani safe havens and sent US commandos to kill jihadist king-pin Osama Bin Laden in his Abbottabad hideout.
But Trump's aggressive language -- first in a speech last August and most recently in his first tweet of the New Year -- has angered Pakistani officials.
"The United States has foolishly given Pakistan more than 33 billion dollars in aid over the last 15 years, and they have given us nothing but lies & deceit, thinking of our leaders as fools," Trump wrote.
"They give safe haven to the terrorists we hunt in Afghanistan, with little help. No more!"
Pakistani leaders disputed the $33 billion figure, insisting that around half of the money relates to reimbursements. The prime minister's office accused him of ignoring the great sacrifices the country has made to fight extremism.
Pakistan says it has lost more than 62,000 lives and $123 billion in the conflict since 2003, and the military insists it has now eradicated militant safe havens.
Privately US diplomats insist that the relationship is not in crisis, pointing to recent visits to Pakistan by secretaries of state and defense Tillerson and Mattis.
They say Pakistan is not refusing to fight the Haqqani network, but that the two capitals disagree about the facts on the ground, with US intelligence still seeing militants operating freely.
- 'Aggressively confront' -
Nauert was at pains to point out that the frozen funds had not been cancelled, and would be ready to be disbursed if Pakistan takes action to prove its commitment to the fight.
"The United States stands ready to work with Pakistan in combating all terrorists, without distinction," Nauert said.
"And we hope to be able to renew and deepen our bilateral security relationship when Pakistan demonstrates its willingness to aggressively confront the Afghan Taliban, the Haqqani Network and other terrorists and militant groups that operate from within its country.
"So we will not deliver military equipment or transfer security-related funds to Pakistan unless it is required by law," she said.