NAYPYITAW, Myanmar — Myanmar's ethnic Kokang rebels are being supported in their fight against government forces by allied minority rebel groups and former Chinese soldiers recruited as mercenaries, a senior military officer said Saturday.

Speaking at a news conference in the capital, Naypyitaw, Myanmar's chief of military affairs security said that despite the assistance, the Kokang guerrillas were retreating after about two weeks of combat. Lt. Gen. Mya Tun Oo said the government was forced to fight because it needed to defend its sovereignty over Kokang, a special region near the border with China.

The army had to act because the Kokang "tried to grab power from the elected local administration," he said. "Since this is an attack on part of our territory, the army will not yield to such an attempt."

More than 50 troops and 70 Kokang rebels have been killed in fighting since Feb. 9, according to the government.

Mya Tun Oo said the Kokang were being helped in combat by guerrilla armies from the minority areas of Kachin, Mong La, Wa, Palaung and northern Shan. Kachin and Wa rebels field relatively powerful forces, but the Kachin have denied taking part in combat in Kokang.

Mya Tun Oo also said the Kokang forces included former Chinese soldiers who were providing military training. Myanmar officials had previously suggested that the Kokang had support from China — a claim denied by Beijing. The Kokang are ethnically Chinese, and their leaders have sheltered on the Chinese side of the border.

China is a major political and economic supporter of Myanmar, but there is unease among many about the influence the Chinese exercise, especially in loosely controlled areas in the north.

Also Saturday, a wider range of ethnic rebel groups issued a statement of moral support for the Kokang.

The United Nationalities Federal Council said the Kokang shared the demands of the members of the coalition for greater autonomy from the central government. The UNFC urged the government to make peace with the Kokang through current multilateral negotiations that they hope will lead to a political settlement with all the groups.

The government on Tuesday announced the imposition of a 90-day state of emergency and military administration for Kokang. The declaration of military administration gives the army executive and judicial authority in the region.

The fighting has also forced tens of thousands of civilians to flee over the border into China.