Mexican soldiers have raided the offices of federal anti-drugs police in what is being described as the biggest strike against police corruption there in recent years.

The operation was aimed at combating impunity and corruption within the Justice Department, an official said.

President Fox is cracking down on drug trafficking and corruption

Thursday's raids follow the arrest last weekend of seven drug agents in the border city of Tijuana - they were charged with drug trafficking, extortion and kidnapping.

They were arrested by Mexican soldiers for holding more than four tons of marijuana which had not been registered with the authorities.

The agents had illegally detained two drug smugglers and had then offered to free them, and give them back their drugs, in exchange for $2m, the attorney general's office said.

Hundreds investigated

Attorney General Rafael Macedo de la Concha said Thursday's operation was not a reaction to the problem in Tijuana, but part of a "planned strategy".

"This allows us to start the work of restructuring... with a new special prosecutors' office whose personnel will be subject to previous review and screening," he said.

Heavily-armed soldiers took control of offices in the states of Sonora, Chihuahua, Tamualipas, Nayarit, Chiapas, Guerrero, Baja California, Oaxaca, Tabasco, Yucatan and Jalisco.

There were no reports of arrests in the raids, but officials said that hundreds of federal agents were already under investigation for corruption.

Justice Department spokesman Angel Buendia said that 1,180 such cases had been investigated since 2000.

President Vicente Fox took office in 2000 with a pledge to crack down on corruption and drug trafficking.