Two US soldiers have been killed in a gun battle in south-eastern Afghanistan, the US military has said.
Six Afghan and two other American troops were slightly wounded in the exchange, in the province of Paktika.
Meanwhile Nematullah Shahrani, one of President Karzai's four deputies, has escaped an apparent assassination bid.
The attacks come amid security fears for October elections which militants opposed to the US-backed Kabul government have pledged to disrupt.
Kunduz Governor Mohammad Omer said that one of the drivers in Vice-President Shahrani's convoy was slightly injured when a remote-controlled bomb hit his vehicle in the northern province's Khanabad district.
Mr Karzai himself came under rocket attack from Taleban militants in Paktika last Thursday, and was forced to abort his trip.
The American military has given few details about the latest incident in Paktika, but says the injured soldiers were evacuated to a base in a neighbouring province.
The area where the clash occurred borders the Pakistani tribal area of South Waziristan, where Pakistan's armed forces had been engaged in heavy fighting with militants.
US-led forces frequently clash with militants in border areas
The BBC's Andrew North in Kabul says many cross back and forth into Afghanistan, and confrontations with US forces are a frequent occurrence.
There were also reports of clashes on Monday between US-led forces and suspected militants in Uruzgan and Zabul provinces, which are both said to have high concentrations of Taleban militants.
US-led forces have around 18,000 troops in Afghanistan hunting militants in the south and east Afghanistan. The vast majority are American.
Another 1,100 US soldiers from the 82nd Airborne division are being sent ahead of the elections.