At least two explosions were heard in the Afghan capital Kabul on Wednesday shortly after US President Barack Obama paid a surprise brief visit to the country.
One of those explosions was a suicide car bomb that struck the Jalalabad road area, which is home to several foreign military bases, Kabul's police chief Mohammad Ayoub Salangi told AFP.
There were no immediate details on casualties or the target, he said.
The US embassy, which neighbours the AFP bureau in Kabul, said its embassy was "under lockdown" and warned staff to "take cover, move away from the windows".
Obama earlier dropped from night skies into Kabul amid secrecy and tight security and signed a deal with President Hamid Karzai, cementing 10 years of US aid for Afghanistan after NATO combat troops leave in 2014.
"Duck and cover here at the embassy. Not a drill - avoid the area," the US embassy said on Twitter.