The Briton, who has not been named, was working for a foreign company building a road from the southern city of Kandahar to the western city of Herat.

At least three policemen were killed when the convoy the two were travelling in was attacked yesterday in western Afghanistan.

Major Andrew Elmes, a spokesman for a Nato-led peacekeeping force in the region, confirmed that a Briton had been abducted and said: "We are now standing by ready to give any assistance." He said Nato troops had set up checkpoints in the area and were searching for signs of the abducted pair.

A Foreign Office spokeswoman said: "We are aware an incident has taken place in Afghanistan as a result of which a UK national is missing and we are urgently seeking further details from the Afghan authorities."

The local police chief, Allah Uddin Noorzi, said a Filipino employee of the same company who escaped the attack had been found hiding under a bridge.

The police chief blamed the Taliban for the man's disappearance but an interior ministry spokesman, Latfullah Mashal, said it was the work of a criminal gang.

He said no contact had been made with the kidnappers and that a delegation from Kabul was hurrying to the area.

The kidnappings come just weeks after a Lebanese engineer building another road in southern Afghanistan was abducted. He was released unhurt days later.

Militants have stepped up attacks ahead of elections on September 18 and more than 1,100 people have been killed in the past six months.