Seven Afghans, including two children, have been killed and five injured in three separate incidents in Afghanistan.

A roadside bomb exploded late on Friday in southern Kandahar province killing two children, said Interior Ministry spokesman Lutfullah Mashal.

Another explosion on Friday blew up a tractor-trolley in the northern provincial capital Mazar-i-Sharif, leaving two dead and five wounded, Mashal said.

Authorities said they had no immediate clues as to who might have carried out the attacks, but such incidents have previously been linked to Taliban fighters.

Drivers killed

Suspected Taliban fighters also ambushed a convoy of civilian trucks carrying vehicles to the US military in southern Afghanistan, killing three of the drivers.

The armed men attacked the trucks on Friday after they crossed the Pakistani border at Spin Boldak, 90km (55 miles) south of Kandahar city, Spin Boldak District Chief Fazeluddin Agha said.

Three of the drivers - two Pakistanis and one Afghan - were killed in a hail of gunfire that severely damaged the trucks and two of the military vehicles, Agha said.

He did not identify the types of vehicles being transported.

The fourth driver escaped and told authorities that four armed men had appeared in front of the convoy and opened fire, Agha said.

Agha blamed Taliban fighters for the attack, but provided no evidence to support his claim.

A spokeswoman for the US military in Kabul said she was unaware of the incident.

There has been a resurgence of attacks since the end of the harsh Afghan winter, countering statements from US commanders and Afghan officials that the country is secure more than three years after the former Taliban government was driven out.

PHOTO CAPTION

US soldiers patrol in Parwan north of Kabul on March 14. At least four US soldiers were killed in an explosion in the southeastern Afghan province of Logar when their vehicle convoy ran over a mine. (AFP)