The Taliban say they have captured two US servicemen in Afghanistan, and Nato confirmed they were missing and scrambled helicopters and planes to search for them.

The US and Nato-led International Security Assistance Force (ISAF) said the pair had gone missing after leaving their base in the capital in a vehicle on Friday.

The only other ISAF service member believed held by the Taliban is Idaho National Guardsman Bowe Bergdahl, whose capture in June last year triggered a massive manhunt. His captors have repeatedly issued videos of him denouncing the war, in what the US military has called illegal propaganda.

Last month was the deadliest of the nine-year war in Afghanistan for foreign troops, with more than 100 killed. Five ISAF service members were killed in across the country on Saturday, including four by one roadside bomb.

"Two International Security Assistance Force service members departed their compound in Kabul City in a vehicle on Friday afternoon and did not return," ISAF said in a brief statement.

"The unit dispatched vehicles and rotary-winged assets to search for them and their vehicle, and the search is ongoing."

A Taliban spokesman said that insurgent commanders had reported the pair was being held and that a third servicemen had been killed. The ISAF statement did not mention a third service member.

Local radio in Logar, a short but dangerous drive to the south, broadcast appeals from ISAF commanders for information about the two and offering a $20,000 (12,956 pound) reward.

"Early this morning two coalition personnel went missing. They are believed to have been captured by insurgents somewhere in Logar province," the broadcast said.

"They may have been separated from one another or may be in the process of being moved to another location."

The statement on local radio described the missing service members as US personnel, last seen wearing standard US military camouflage.

One was described as about six feet (183 cm) tall weighing 220 lb (100 kg) with blond hair and brown eyes. The other was described as 190 lb (86 kg), bald with a thin moustache. Both men have tattoos, the broadcast said.

"Coalition forces are offering US$20,000 reward for any information that leads to the successful return of these two," the radio broadcast said, providing a contact number and no further identification of the men.