Taliban militants say international forces have violated a US-Taliban agreement to withdraw their forces from Afghanistan by May 1, and that this "opened the way" for the group to retaliate.
A formal withdrawal of US and NATO forces began on Saturday, due to be completed by September 11, although military equipment had already started leaving the country weeks ago.
After 20 years of international troops' presence, the withdrawal leaves Afghanistan to an uncertain future amid rising attacks by Taliban insurgents.
The Taliban said on Saturday that the withdrawal was too late.
The "agreed upon May 1st deadline has passed," the Taliban said in a statement tweeted in English.
"This violation in principle has opened the way for IEA (Islamic Emirate of Afghanistan - name used for the country by the Taliban) Mujahidin to take every counteraction it deems appropriate against the occupying forces," it said.
The group said that their fighters would now await a decision from their leadership "in light of the sovereignty, values and higher interests of the country".
The Taliban had signed a deal with previous US president Donald Trump that specified troops would be gone from the country by May 1 subject to certain security guarantees.
Almost 10,000 NATO soldiers from the Resolute Support training mission - including 2500 soldiers from the US and about 1100 from Germany as the two biggest contingents - are now due to leave the country by September 11.
The German military said earlier this month it was planning a more rapid withdrawal, perhaps by the start of July, but a date has not been confirmed.
There are fears the Taliban might attack the forces during the withdrawal.
A NATO official said any attacks would be met with a forceful response.
The withdrawal of the international forces will be a test for the Afghan security forces, which will have to defend the territory it currently controls and support the government without direct international support.
The violence continued in the country on Friday and Saturday, with a car bombing and a blast inside an Afghan base killing more than two dozen people.
Later on Saturday, there was indirect fire on Kandahar airfield in the south of Afghanistan where some US forces are still stationed.
"A return to violence would be one senseless & tragic. But 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. That would be a mistake to move in that direction," US army spokesman in Afghanistan Colonel Sonny Leggett tweeted.