MAKHACHKALA, Russia (AP) _ Russia's Defense Ministry assumed full control today over military operations against Islamic militants in southern Russia, a signal that existing units were having trouble rooting out the rebels.

Russian aircraft and artillery pounded rebel positions in the southern republic of Dagestan, but heavy rain limited the scope of the attacks, the military said.

The Russian forces, led by Interior Ministry troops, have been battling several hundred rebels in about a half-dozen villages and surrounding hills for the past seven days.

With superior manpower and firepower, the Russians have the upper hand, but they have not been able to defeat militants who have hunkered down in well-entrenched positions they built long before the fighting began, witnesses said.

The Interior Ministry troops have been in charge of the operation, but the Defense Ministry was given full control today, and army Lt. Gen. Gennady Troshev was appointed commander of the unified forces.

No reason was given for the move. However, the Russians have relied on a mishmash of units to combat Islamic militants in the Caucasus region in recent years, and that has often created coordination problems.

The Russian forces have included army ground troops, the air force, Interior Ministry soldiers, local police forces, and in some cases, volunteers who were provided weapons but received little or no training.

All of these forces took part in last month's fighting against militants who seized several mountain villages in western Dagestan, just inside the border from the breakaway territory of Chechnya.

The Russians drove the rebels out after two weeks of often heavy fighting, and are now trying to round up rebels in and around the central village of Karamakhi, a stronghold for militants who want to create a separate Islamic state in southern Russia.

The militants, members of the fundamentalist Wahhabi sect, took control of Karamakhi and nearby villages a year ago and began imposing their interpretation of strict Islamic law.