ISLAMABAD, July 11: Mortar shells fired from Afghanistan wounded at least six Pakistani security personnel along the border, and Pakistan had lodged a “strong protest” with Nato, the army’s top spokesman said on Friday.

The six mortars were fired overnight and fell close to a military post in the town of Angoor Adda in the South Waziristan tribal region, Maj-Gen Athar Abbas said.

Pakistani forces immediately returned fire, and “casualties were reported on the other side,” he said.

“This was mortar fire from the Afghan side,” Gen Abbas said. “Whether it was foreign forces or Afghan forces it’s yet to be determined.”

Asked if militants across the border could have been behind the firing, Gen Abbas said he did not want to speculate. US military officials in Afghanistan did not immediately respond to requests for comment.

Details — such as the exact time of the incident — remained sketchy on Friday night.

The clash comes about a month after another border incident, in which Pakistan said 11 of its soldiers died when US aircraft bombed their post in the Mohmand area.

Afghan and Pakistani troops have skirmished repeatedly on the long, poorly demarcated border, despite urgings from US officials that they improve their coordination.

(Our Correspondent in Wana adds that the shells fired from across the border hit the Zera Laita checkpost at about 2am on Friday. The post was destroyed.

An official said the injured soldiers were airlifted to a hospital in Bannu. Local people said that eight shells had hit several other areas near the border.)

Meanwhile, pilotless US drones armed with missiles have stepped up patrols over villages on the Afghan-Pakistan border, fraying nerves below.

Villagers living on the frontier call them “buzzers”, and the aircraft have increasingly taken to the skies, causing sleepless nights and occasionally raining down death.“We’re sick of these drones, they’re driving us crazy,” said Sher Shah, a government official in the town of Wana. “They fly so low at night we can’t sleep!”

The Predators, capable of carrying two anti-tank Hellfire missiles, can remain aloft for up to 24 hours --- providing the Central Intelligence Agency with a wealth of intelligence beamed live from its hi-tech cameras.

They have struck several times in northwest Pakistan this year, killing dozens of suspected militants.

Sometimes villagers can spot the drones --- a tiny speck in the sky --- and even fire at them with rifles. At other times the drones are too high to see, but you know they’re there from the distinctive and incessant buzz given off by their rear-mounted propeller engines.

The buzzing often gets louder at night as the drones patrol at lower altitudes in the darkness, villagers say.

Residents of Bajaur, a region on the Afghan border to the northeast of Waziristan, said drones flew overhead all night on Thursday.

“The sky is not safe, the earth is not safe, where should we go?” asked Jabbar Shah, a resident of Inayat Kalay village, about 10km from the border.

“We don’t know when will they strike and who will they hit. It’s very worrying,” he said.

—Agencies