The United Nations says four attacks have taken place against U.N. peacekeepers in Mali's northern Kidal region but there were no casualties.

U.N. spokesman Stephane Dujarric said three separate U.N. camps in Aquelhok, Tessalit and Kidal came under rocket and mortar attack Tuesday morning and two reported minor structural damage.

He said "search operations in pursuit of the perpetrators are ongoing."

Dujarric said the U.N. mission also reported that peacekeepers on patrol in Kidal City were fired on Tuesday morning.

He said the attacks "constitute war crimes under international law."

The more than 11,000-strong mission in Mali has become the most dangerous in the world for U.N. peacekeepers, who are routinely attacked by Islamic militants across the north.