In a written statement issued after Kurdish rebels killed at least 24 soldiers in simultaneous attacks in southeast Turkey, Ban's spokesman Martin Nesirky said the sovereignty of both Turkey and Iraq must be respected.

"The secretary general expresses his concern over the attacks in the Hakkari province of Turkey, reportedly by Kurdish elements operating from Iraqi territory, which have left many Turkish soldiers dead," he said.

Turkey hit back with cross-border air strikes on rebel bases and sent troops into neighboring Iraq as Prime Minister Recep Tayyip Erdogan canceled a foreign trip and called an emergency meeting of top security officials.

"It is clearly unacceptable that Iraq's territory is being used to mount cross-border attacks against neighboring countries," Nesirky said.

"The secretary general urges Iraq and Turkey to engage in constructive dialogue in order to find a peaceful solution to this challenge."