Police killed three potential suicide bombers in Afghanistan's volatile east on Tuesday after the attackers stormed a government building and a gunfight was continuing against a fourth assailant, authorities said.

Two policemen were killed in the firefight, the ministry of the interior said. The Taliban claimed responsibility for the attack in Paktika province, which shares a porous and ill-defined border with Pakistan.

The four insurgents, with small explosives strapped to their bodies and carrying grenade launchers, targeted the government communications office near the home of the Paktika governor Mohebullah Samim.

One policeman was killed and part of the communications building is now on fire, Samim told Reuters, adding the fourth insurgent was still resisting.

Troops from NATO's International Security Assistance Force (ISAF) were providing air support, he said.

Taliban spokesman Zabihullah Mujahid said in an emailed statement the group's fighters had occupied the communications building and killed U.S. nationals, but the Islamist group often exaggerates accounts of engagements and casualties.

Eastern Afghanistan has seen increased violence in recent years, with insurgents taking advantage of the steep, often forested terrain and the Pakistani border to launch attacks and then slip back beyond the reach of NATO and Afghan troops.

Despite the presence of more than 100,000 foreign troops, violence across Afghanistan remains at its worst levels since the Taliban were toppled by U.S.-backed Afghan forces in late 2001, according to the United Nations.

(Writing by Amie Ferris-Rotman; Editing by Paul Tait)