Kabul: Three female international aid workers were killed on Wednesday in an ambush by insurgents in southern Afghanistan, a provincial governor said.

The aid workers were driving to the capital when they were attacked on a road near the town of Pul-i-Alam.

A car cut in front of them and then opened fire.

The attack happened in Logar province, which lies to the south of Kabul, Logar's governor Abdullah Wardak said.

The international group said to employ the four could not be reached for confirmation.

There was no immediate claim of responsibility for the incident, the deadliest in years involving international aid workers.

Taliban insurgents regularly carry out attacks across the country, but bandits and other criminals are also blamed for a growing wave of violence.

Aid workers said in a report this month that 19 of their number had been killed in Afghanistan this year, with worsening security fears causing them to cut back relief work.

"Aid organizations and their staff have been subject to increasing attacks, threats and intimidation, by both insurgent and criminal groups," the Agency Coordinating Body for Afghan Relief said in a statement earlier this month.

This year there have been over 84 such incidents, including 21 in June, it said, more than in any other month in the last six years.