NAYPYITAW (Reuters) - Myanmar's Parliament voted on Tuesday to again extend martial law for three months in a restive area along the country's border with China, where there have been clashes between the military and an armed ethnic group since February.

Cross-border incidents in the fighting have strained ties between the neighbours.

They have also proved problematic for President Thein Sein, who has ambitions to sign a nationwide ceasefire with many of the country's armed ethnic groups before a general election on Nov 8.

On Tuesday, a majority of Parliament members backed the motion to continue martial law in the Kokang region of Shan state. Martial law gives the military sweeping judicial and administrative powers.

The measure was needed because of continued instability in the region, said Shwe Mann, the embattled speaker of parliament.

President Thein Sein declared a three-month state of emergency and imposed martial law in the region on Feb. 17 after fighting broke out between the Myanmar military and the Myanmar National Democratic Alliance Army (MNDAA).

Parliament voted to extend martial law for the first time in May. The MNDAA declared a unilateral ceasefire the following month after coming under pressure from Beijing to end the conflict, but clashes have since been reported.

The MNDAA was formed from remnants of the Communist Party of Burma, a powerful China-backed guerrilla force that battled the Myanmar government until it splintered in 1989.

The government has excluded the group, and two other armed ethnic forces that fought beside it, from the peace process. Some of the other ethnic groups negotiating the peace pact would like the groups to be included.

The armed ethnic groups are meeting on Friday in Chiang Mai in Thailand to discuss their next moves.