US Colonel Rodney Davis said one soldier was slightly injured from bumping his head in a vehicle during the contact in Khost but was treated at the scene.
"A Special Operation Forces convoy north of Bari Kott in Khost province received small-arms fire and two RPGs from an unknown-sized enemy forces yesterday morning," Davis told reporters at Bagram Air Base 50 km north of Kabul.
In a separate incident, Special Operation Forces came under smalls-arms attacks from unknown gunmen on Thursday in the north-eastern city of Konduz. There were no recorded injuries.
"A patrol was sent out this morning to investigate the area from where the shots were fired," Davis said, without giving any more details.
With most of the militias targeting US bases in the south-eastern border region, it is the second attack on US forces in Konduz in less than a month.
Meanwhile, Davis added that a rocket was fired at a US base in south-western Kandahar province but it did not go off.
He did not say which groups were suspected of carrying out the attacks but similar incidents have been blamed on Taliban remnants and their allies from Osama bin Laden's al-Qaeda network, or fighters loyal to former Afghan premier and commander Gulbuddin Hekmatyar.
In other developments:
A provincial governor also said on Friday that several Afghan opposition leaders, including senior members of the ousted Taliban, have met near the Pakistani border to plot coordinated attacks on government and foreign troops and aide workers.
The governor said Gulbuddin Hekmatyar and two commanders of the ousted Taliban – Jalaluddin Haqqani and Saifur Rahman – drew up the strategy at a meeting in Pakistan's tribal area near the Afghan border.
Gulbuddin Hekmatyar is thought
to be behind attacks against US
"We have reports they met recently and talked over launching coordinated attacks," the governor of Ghazni province, Haji Assadullah, told the Reuters news agency.
All three opposition leaders are on a US military wanted list. Assadullah said he did not know exactly when or where the meeting took place.
The rebels planned assaults in Wardak and Ghazni provinces southwest of Kabul and in southeastern Paktika, Paktia and Khost provinces, Assadullah said.
Assadullah also said government forces could confront and foil any conventional attack, but the rebels could launch hit-and-run strikes.
"They do not have the ability to carry out large-scale attacks. They are not a serious threat," Assadullah said. "But I think we may see an increase in the sort of terrorist attacks we've been seeing."
Some 19 months after the toppling of the Taliban, remnants of the former government and its al-Qaeda allies continue to launch regular attacks on US and pro-government forces mainly in the southern and eastern provinces bordering Pakistan.
A US-led coalition force of some 11,500 troops is currently hunting down Taliban and al-Qaeda hold-outs in the south and east of country.