Four Pakistanis including two children were wounded on Monday when a mortar shell fired from Afghanistan struck a village near the border, Pakistani security officials said.
It was the latest incident in a series of alleged cross-border attacks that have raised tensions between the neighbours as officials confirmed exploratory peace contacts between Afghanistan, the United States and the Taliban.
The officials said the shell hit Bangedar village in the Ghulam Khan district of North Waziristan, the region where America has long called on Pakistan to launch an operation against Taliban and Al-Qaeda-linked militants.
"The fire came from an Afghan border post in Khost province (in eastern Afghanistan) early this morning," said local government official Mohammed Khan.
"One injured person is in a critical condition," said doctor Mubarak Khan at the main hospital in Miranshah, adding that two children aged eight and 13 were among those wounded.
In Kabul, around 200 Afghans protested on Saturday against Pakistani rocket attacks that officials say have killed dozens of people.
Last week, Afghan President Hamid Karzai demanded an end to the attacks when he met the head of Pakistan's army, General Ashfaq Kayani, in the Afghan capital.
Pakistan said only that its security forces may have fired a few accidental rounds into Afghanistan while pursuing militants across the porous 2,400 kilometre (1,500 mile) border.
There are Taliban strongholds on both sides of the border, but Afghan and US officials want Pakistan to do more to eradicate militant sanctuaries in its semi-autonomous tribal belt used to launch attacks in Afghanistan.