At least five militants were killed Tuesday when a US drone fired missiles on a compund in Pakistan's restive tribal region, taking the death toll to 18 after three strikes in three days, officials said.

The latest attack targeted a home in the Shawal district in South Waziristan, a tribal region bordering Afghanistan which is considered a stronghold of Taliban insurgents.

"A US drone fired three missiles targeting a house, killing five militants," a senior Pakistani security official told AFP.

Another security official confirmed the attack and said the identity of those killed was not yet known.

He added that the death toll from a drone strike in the same area on Monday has climbed to eight. Another attack the previous day killed five militants, authorities have said.

The semi-autonomous tribal region has for years been a hideout for Islamist militants of all stripes -- including Al-Qaeda and the homegrown Tehreek-e-Taliban Pakistan (TTP) as well as foreign fighters such as Uzbeks and Uighurs.

Washington pressed Islamabad for years to wipe out sanctuaries in the North Waziristan tribal area, which militants have used to launch attacks on NATO forces in Afghanistan.

The Pakistani military launched a major anti-militant offensive in North Waziristan in June and say they have killed more than 1,000 so far, with 86 soldiers losing their lives in the operation.

The area is off-limits to journalists, making it impossible to verify the number and identity the dead independently.

Pakistan routinely protests against US drone strikes, which have been targeting militants in the tribal areas since 2004, saying they violate its sovereignty and are counterproductive in the fight against terror.

But most analysts believe the resumption of the drone programme after it was suspended -- reportedly to give Pakistan space for negotiations with the Taliban -- is evidence of collusion between the two countries.

The Islamabad government and military officials strongly deny this.