GENEVA (Reuters) - Three children were killed and one person was wounded in an air strike on the capital of the Tigray region in Ethiopia on Monday, the United Nations cited local health workers as saying.

       The health workers said the casualties were caused in the strike on the outskirts of Mekelle, Jens Laerke, spokesperson of the U.N. Office for the Coordination of Humanitarian Affairs (OCHA), told a briefing in Geneva on Tuesday.

       A second air strike in the city wounded nine people and damaged houses and a hotel, Laerke said.

       "This escalation of the conflict is very alarming," he said.

       Rebellious Tigrayan forces accused the Ethiopian government of launching air strikes on Mekelle on Monday, and though a government official initially denied strikes, state-run media later reported the air force conducted an attack.

       Ethiopia's government spokesman, Legesse Tulu, did not immediately respond to phone calls requesting comment on the U.N.'s report that the three people killed in Monday's air strike were children.

       The reported raid follows intensified fighting in two other Ethiopian regions, where the central government's military is trying to recover territory taken by the Tigrayan People's Liberation Front (TPLF).

       Tigrai TV, controlled by the TPLF, said the attack on the city of Mekelle killed three civilians.

       War erupted in Tigray almost a year ago between the Ethiopian military and the TPLF, the political party that controls the northern region, killing thousands of people and forcing more than 2 million to flee.

       (Reporting by Emma Thomasson, additional reporting by Nairobi newsroom; Editing by Stephanie Nebehay and Alex Richardson)