Secretary of State John F. Kerry talks to the media following the NATO Foreign Affairs Ministers meeting held at NATO headquarters in Brussels, on Tuesday. (THIERRY CHARLIER/AFP/Getty Images)

Time and patience are running out for countries planning to help support Afghanistan’s military after NATO-led troops depart, NATO and U.S. officials warned Tuesday.

Meeting in Brussels with Afghanistan’s interior minister and its senior diplomat, NATO officials made clear that they cannot leave even a small contingent of forces behind without guarantees that Afghan President Hamid Karzai is refusing to give.

“This is not fooling around. This is serious business. There are over 50 nations who are engaged here through NATO in trying to help Afghanistan,” Secretary of State John F. Kerry told reporters. “Those nations have budget cycles; those nations have planning requirements. Those nations have equipment requirements; they have deployment requirements. All of those things are best managed through planning.”

Karzai balked last month at signing a security deal with the United States that governs U.S. support and obligations after most international forces leave next year. A similar agreement covering NATO forces was expected to piggy­back on the U.S. deal, which Karzai has suggested he won’t sign before spring. The Obama administration wants it signed by Dec. 31.

“It is clear that if there is no signature on the legal agreement, there can be no deployment, and the planned assistance will be put at risk,” NATO Secretary General Anders Fogh Rasmussen said.

Rasmussen declined to specify a deadline for a NATO decision but said planning for troop commitments takes time, money and, in some cases, parliamentary approval.

“I have to remind everybody that there are certain realities on the ground,” for nations that would send forces, he said. “Those facts on the ground make it necessary to sign that legal framework very soon.”

U.S. officials have said that the United States and NATO could keep 8,000 to 12,000 troops in Afghanistan after 2014. The U.S. contingent would be partly responsible for training and advising Afghan forces and partly focused on U.S. counterterrorism priorities.

National security adviser Susan E. Rice traveled to Kabul last week to tell Karzai that there was no room for delay or renegotiation of a deal that has been a year in the making. She came away empty-handed, and Karzai has appeared to harden his opposition despite overwhelming approval of the pact by a tribal council he helped select.

Kerry was meeting with the Afghan officials alongside other NATO foreign ministers over two days of talks here. His frustration was clear seven weeks after he made an emergency trip to Kabul to negotiate the bilateral deal with Karzai. Kerry laid blame on Karzai for changing the terms afterward.

“I don’t believe in renegotiating unilaterally,” he said. “And I don’t think President Obama appreciates, [after] the amount of sacrifice that has been made by our troops, by the American people, to contribute to the future of Afghanistan, that this stuff now is being left in doubt at this critical moment.”

Also Tuesday, the Pentagon announced that the U.S. military has temporarily halted ground shipments of cargo leaving the war zone along a primary supply route into Pakistan. Spokesman Mark Wright said military logisticians decided to stop the shipments through the Torkham Gate border crossing because local drivers working for the U.S. military were being targeted by Pakistani protesters angry about American drone strikes.

Wright said he did not expect any “long-term impact” on the drawdown of military equipment from Afghanistan. The U.S. military also moves smaller amounts of ground cargo via another border checkpoint, in southeastern Afghanistan, as well as by air. The ground routes are far cheaper, however. Wright said the Pentagon expects to resume traffic through the Torkham Gate “in the near future.”

Craig Whitlock in Washington contributed to this report.