Pakistani officials say unknown attackers have hurled a grenade into a mosque in a tribal region bordering Afghanistan, killing two people and wounding four others.
Local authorities say it was not immediately clear who was behind Thursday's attack in a village in semi-autonomous South Waziristan.
They say police have detained several Afghan refugees living in the area for questioning.
In March 2004, Pakistan deployed more than 70,000 troops in its tribal areas bordering Afghanistan in an effort to flush out al-Qaida-linked militants and their local allies. The area is also considered a possible hideout for al-Qaida leader Osama bin Laden.