Secretary General Ban Ki-moon is seeking some 2,500 more peacekeepers to reinforce the United Nations mission in Mali which has seen 12 of its members killed in May alone.

Spokesman Stephane Dujarric said Thursday the troops would include a rapid reaction force and specialists in high security convoys among other things.

"I think it's clear to everyone that the security situation in parts of Mali have deteriorated. I think the U.N. staff have paid for it in blood," he said.

On Tuesday, one U.N. peacekeeper from China was killed and three others were gravely wounded in an attack on the mission's camp in the city of Gao.

The Security Council is set to consider Ban's request when it votes on whether to extend the mission's mandate on June 29.