WANA: Missile strikes from two US drones killed at least 21 suspected militants in Pakistan's South Waziristan on Monday, Pakistani officials said, part of an intensified US assault in the tribal belt this month.

In the first strike, a missile hit a moving vehicle in Ghalmandi Panga village on the Afghan border, killing eight militants.

A few hours later, another drone fired three missiles into a militant training centre in Mantoi town, about 30 km north of South Waziristan's main town of Wana.

“It was a big compound which was used as training centre. Militants have cordoned off the area and bodies are being removed from the rubble,” an intelligence official in the region, who declined to be identified, told Reuters.

Thirteen militants were killed in the second strike. Another official said militant casualties could rise. There was no way to verify the deaths independently. Militants often dispute official casualty tolls.

US forces have stepped up strikes by remotely-controlled drones in Pakistan's border regions since the killing of Osama bin Laden by US forces in the country last month.

Eighty-eight militants have been killed by US drones this month, according to a Reuters tally based on statements from intelligence officials.

Pakistan publicly opposes drone attacks, saying it complicates its efforts to fight militants who want to topple the pro-US government and impose strict Islamic rule in the country.

The United States has been pushing Pakistan to step up its war against militants who carry out attacks on Western forces in Afghanistan from their bases in Pakistan's tribal belt.