Pakistan on Monday protested to the Afghan government over a militants' cross-border attack on a checkpost, which killed at least 6 Pakistani soldiers, according to local media.

Security officials said that Pakistani Taliban militants now operating from the border regions in Afghanistan Sunday attacked a checkpost in Upper Dir district and killed 6 soldiers.

A spokesman for Pakistani Taliban Siraj-ud-Din claimed in phone calls to the media in Pakistan responsibility for the attack and said 17 Pakistani soldiers were killed.

Siraj-ud-Din said that Maulana Fazalullah, the former chief of Taliban in Swat valley, is now leading his fighters in border regions of Afghanistan and also issues instructions to their remnants in Swat and nearby areas.

Adviser to Pakistani Prime Minister on interior affairs, Abdul Rehman Malik expressed his grievances to Afghanistan over the Afghan militant attack on Pakistani security personnel in Upper Dir area, local TV channels reported.

Malik contacted the Afghan Interior Minister to register his complaint over the incident and "blamed Afghan authorities for not preventing the cross border movement of militants into Pakistan", Dawn TV reported.

Local media put the death toll at 10 while 10 more had been missing since the Sunday attack.

Security sources said that Pakistan forces killed 15 militants in retaliatory action.

The security forces' team was patrolling on the Pakistan- Afghanistan border when it was attacked by the militants who crossed the border, local reports said. The sources said that the team was sent to gather information of militant presence in the area.

Pakistan insists that several top Pakistani Taliban leaders, including Fazalullah, Maulvi Faqir of Bajaur tribal region and Abdul Wali from Mohmand tribal agency, have established bases in Afghanistan and regularly launch attacks on Pakistani border posts from there.

Pakistani Taliban in a major cross-border attack in August last year had killed 25 security men in northern Chitral district.

Afghan government denied Islamabad's assertions, but a senior Pakistani official disclosed this month that the Afghan government has now admitted presence of Pakistani Taliban in remote Afghan areas.

Also on Friday, two Pakistani security men were killed and two others were injured when a mortar shell hit a border post in Mohmand Agency, official sources said. The sources said a rocket was fired by militants from across the Pakistan-Afghanistan border, which struck the post in Khwezai region.