BEIJING - For more than a month, war has raged in a remote area of northern Myanmar between ethnic Chinese rebels and Myanmar government forces. The fighting, after five years of calm, has left several hundred soldiers and insurgents dead - and is now spilling beyond Myanmar's border.

On Friday, a Myanmar air force plane strayed over the border and dropped a bomb in China's Yunnan province, killing four people in a sugar-cane field and injuring nine others. Last weekend, Myanmar also bombed Chinese territory, damaging a house. Tens of thousands of refugees have crossed from the Kokang region of Myanmar into China, many sheltering in camps set up by the Chinese Red Cross.

Awkward

The fighting has put Chinese leaders in an increasingly awkward position. The Kokang rebels speak Mandarin and have deep commercial and personal connections in Yunnan. Many ethnic Chinese in the Kokang region complain of being treated like second-class citizens by their government, and the rebels are fighting for more autonomy from the central government.

But China has for years insisted that it adheres to a policy of noninterference in other countries' "domestic affairs"- and insists that other nations do likewise.

Chinese authorities also view Myanmar as a strategically significant neighbor with abundant natural resources and access to the Indian Ocean. With Myanmar's recent nascent steps toward democratic reform bringing closer ties with Western countries including the United States, China is eager to keep amicable relations with, and strong influence over, its southern neighbor.

Support denied

China says it has not lent any official backing to the rebels in the fighting that began Feb. 9. But Myanmar's chief of military affairs and security, Lt. Gen. Mya Htun Oo, said last month that rebels were recruiting former Chinese soldiers as mercenaries. Myanmar's information minister, U Ye Htut, called on Beijing to rein in Yunnan officials who might be offering support.

After Friday's bombing in Licang, China's vice foreign minister, Liu Zhenmin, summoned Myanmar Ambassador Thit Linn Ohn and lodged a complaint. Overall, it was a restrained reaction from Beijing, which often responds with much more umbrage to less provocative moves from neighbors such as Japan that it sees as infringing upon its territory.

The rebels' leader, Peng Jiasheng, 85, has taken to social media to appeal to all those of "common race and roots" for support.

A new round of cease-fire negotiations encompassing a variety of ethnic militias is to resume this week.