BANGKOK, Thailand (AP) _ Thai army units along the border with Myanmar have been on alert since last week in anticipation of renewed fighting between ethnic rebels and Myanmar's military government, Thailand's army commander in chief said today.

``We haven't increased the number of troops, but the troops are on alert and we have rapid reaction forces ready,'' Gen. Surayud Chulanont told The Associated Press.

Hostilities in Myanmar have repeatedly spilled onto Thai soil, with both Myanmar soldiers and the ethnic guerrillas allied with them crossing the border to burn refugee camps throughout 1997.

More than 100,000 mostly Karen refugees are living in camps inside Thailand, having fled what they charge is an ethnic cleansing campaign conducted by Myanmar's military.

The Karen have been fighting for autonomy from the government in Yangon since 1949. In recent years the Myanmar army has dislodged them from most of their bases inside the country.

With the 50th anniversary of their rebellion coming up in January, some rebel leaders expect the army will launch another offensive aimed at wiping them out.

Surayud said that he was seeking permission from the Interior Ministry to move the refugees farther inside Thailand to make it more difficult for invading forces to reach them.

The Thai army, under Surayud's predecessor, Gen. Chetta Thanajaro, was criticized by international human rights groups and Western governments last year for failing to protect the refugees.