Islamabad (PTI): Pakistan on Thursday lodged a "very strong" protest with the US-led coalition forces in Afghanistan after two women and two children were killed in its tribal region by artillery shells fired from across the border.

Five shells fired by the US-led forces in Afghanistan on Tuesday landed on a house in Lwara Mundi town in North Waziristan tribal region, located about two kilometres from the border, killing four persons, army spokesman Maj Gen Athar Abbas said.

Pakistan lodged a "very strong" protest over the incident, Abbas said.

Reports from Afghanistan said a US military spokesman had confirmed the shells were fired as part of a "precision" strike on a target linked with militants.

The US has described Pakistan's lawless tribal areas bordering Afghanistan as "safe havens" for Taliban and al Qaeda militants.

The border is not clearly marked at many places and the ethnic Pashtun tribesmen often cross the porous frontier without any checks.

The US-led forces in Afghanistan launched at least two missile strikes on Pakistan's tribal areas with pilotless drones last month, including one attack that killed top al- Qaeda commander Abu Laith al Libi on February 4.