Six Pakistani civilians and one Afghan soldier were killed on Sunday in cross-border shelling and gunfire, according to officials on both sides of the frontier.

The Pakistan army said Afghan border forces had opened "unprovoked and indiscriminate fire of heavy weapons including artillery/mortar onto the civilian population" at the Chaman border crossing, which links Pakistan's western Balochistan province with Afghanistan's southern Kandahar province.

Six civilians were killed and another 17 wounded on the Pakistani side by the Afghan fire, leading Pakistani troops to retaliate, the Pakistan military said in a statement.

Pakistan's Prime Minister Shehbaz Sharif said the deaths were unfortunate and "deserve the strongest condemnation."

"The Afghan interim government should ensure that such incidents are not repeated," he said in a statement.

The Spin Boldak border of Kandahar province in Afghanistan reopened after being closed for a day, according to the Afghan local media. The border was reopened after talks between the Afghan and Pakistani border authorities after it was said to have been closed due to some misunderstanding.

Afghan security sources said the clash started after Pakistani forces demanded Afghan forces stop building a new check post on their side of the border.

Kandahar police spokesman Hafiz Saber said one Afghan soldier was killed and 10 other people, including three civilians, were injured.

Afghan official Noor Ahmad, in Kandahar, told Reuters the situation had returned to normal after the two sides held a meeting.

The busy Afghan border crossing at Chaman, used for trade and transit, was closed for some hours before reopening, officials on both sides said. The crossing was closed for several days last month after similar clashes.

The Afghan authorities have been told that a recurrence of such incidents must be avoided and strictest possible action must be taken against those responsible, Pakistan's foreign office said.

"Such unfortunate incidents are not in keeping with the brotherly ties between the two countries," it added.