The commander of foreign forces in Afghanistan warned it would be a mistake for insurgents to attack international troops in the country after the passing of a May 1 deadline for withdrawal, agreed last year with Taliban militants.
US Army General Scott Miller's comments followed what a US forces spokesman described as "ineffective indirect fire" at an airfield in Kandahar that caused no injuries or damage. The Taliban did not immediately respond to a request for comment on whether it was involved.
Under a February 2020 deal between former US president Donald Trump's administration and the Taliban, foreign forces were to withdraw from the country by May 1, while the militant group held off on attacking foreign troops and bases.
But US President Joe Biden announced last month, after reviewing the situation, that forces would stay in the country beyond May, withdrawing by September 11.
Kabul was braced on Saturday for a reaction from the Taliban, with a visibly increased military presence and security at checkpoints.
A source said the Afghan capital was on "high alert", while military patrols and security were being increased in main cities.
In a video posted to Twitter by a spokesman for US forces in Afghanistan, following Saturday's incident in Kandahar, Gen Miller said it would be a mistake to move towards attacking foreign troops.
"Make no mistake, we have the military means to respond forcefully to any type of attacks against the coalition and the military means to support the [Afghan] security forces," he said.
Sharp rise in violence
Violence against Afghans has escalated in recent weeks, with more than one hundred Afghan security forces personnel killed.
On Friday, a huge blast in eastern Logar killed dozens as they broke their fasts during Ramadan.
It was not clear who was behind the attack, but the government blamed the Taliban.
The Taliban responded to the Biden administration's move with fiery rhetoric and threatened consequences, boycotting a crucial conference in Turkey planned for last month to help jump-start stalling Afghan peace talks.
Officials and Taliban sources say contacts have been maintained to try to get the Taliban leadership back to the negotiating table and agree to the extended foreign troop presence, but no announcement on an extension had been made by Saturday.
Taliban spokesman Zabihullah Mujahid tweeted that the passing deadline meant "this violation in principle has opened the way for (Taliban fighters) to take every counter-action it deems appropriate against the occupying forces".
But he added that fighters were waiting on the decision of Taliban leaders.
Earlier in the week, Mr Mujahid told Reuters that conversations were continuing.
"Discussions between the US and Taliban and ... within the Taliban's leadership are under way whether to extend that or not," he said.
Washington has also warned that if foreign forces were attacked while carrying out the withdrawal they would defend themselves "with all the tools at our disposal".
Experts said the Taliban threats should be taken seriously, but a number of factors meant that full-scale attacks against foreign targets could be averted, as the Taliban continued negotiations.
"We can't rule out attacks," said Michael Kugelman, deputy director of the Asia Programme at the Woodrow Wilson Centre in Washington.
"That said, the Taliban is less likely to attack foreign forces now that it knows there is a specific date when they will be leaving."
