The South African government expressed concern on Monday that the killing of Libyan leader Muammar Gaddafi's son and three of his grandchildren would lead to heightened tensions.

"The attacks on leaders and officials can only result in the escalation of tensions and conflicts on all sides and make future reconciliation difficult," international relations department spokesman Clayson Monyela said in a statement.

"South Africa maintains that the United Nations Security Council Resolution 1973 does not address itself to the assassination of individuals and officials." The resolution authorises UN member states to take "all necessary measures" to protect civilians under threat of attack in Libya.

Libyans must be afforded the opportunity to decide their own leaders in negotiations conducted peacefully and democratically, he said.

The department called for restraint and appealed to Libyan parties to "preserve life and property".

German news agency DPA reported on Sunday that Saif al-Arab Gaddafi, 29, Gaddafi's youngest son, was killed in a Nato airstrike on the capital Tripoli. Libyan government spokesman Mussa Ibrahim told reporters that Gaddafi and his wife survived the attack, although they were in the same house.

Three of Gaddafi's grandchildren were also killed in the attack on Saif al-Arab Gaddafi's house, which was struck by at least three missiles.

Opposition representatives in and outside the country expressed their doubt regarding the incident, arguing Gaddafi might have been seeking to gain sympathy after his call for a ceasefire was rejected.