Tension has flared on the border between Pakistan and Afghanistan after the two sides exchanged artillery and machine-gun fire.

There were no confirmed reports of casualties in the clash that took place late Monday in the North Waziristan tribal region.

The clash came a day after mortar rounds fired from the Afghan side of the border killed a Pakistani soldier and wounded three others in the same mountainous border area.

Pakistani military officials say they are still unclear about who was responsible for the firing from the Afghan side of the border.

On Monday, a Pakistani spokesman said he is certain the shelling did not come from American positions, but is asking for a U.S. investigation because coalition forces are responsible for security along the Afghan border.

Some information for this report provided by AFP.