By THE ASSOCIATED PRESS

MEXICO CITY (AP) -- More than 750 troops and police officers took over the nation's top security prison on Friday after officials repeated warnings that two of hemisphere's most notorious alleged drug bosses had joined forces behind bars.

The federal Public Security Department said the operation at La Palma came after prison authorities ``declared a state of alert because of grave risks to ... some inmates and the possibility of an escape'' at the facility west of Mexico City.

Two recent killings at the prison, where inmates are supposed to be monitored by frequent guard visits and closed-circuit television, created a national scandal and led officials to oust prison administrators.

On Thursday, the top organized-crime fighter at the Attorney General's Office told reporters that two inmates held at La Palma, Osiel Cardenas and Benjamin Arellano Felix, had joined forces to battle another drug gang.

Jose Luis Santiago Vasconcelos said the two were uniting because the Juarez Cartel has been trying to take over areas once dominated by Arellano Felix Tijuana-based operatives and others loyal to Cardenas' Gulf cartel.

The newspaper La Jornada quoted attorneys as saying Cardenas and Arellano Felix were on a hunger strike at the prison to protest tightened security. Officials denied the report.

Santiago Vasconcelos said the control of the Juarez Cartel has shifted away from Vicente Carrillo Fuentes, whose brother, Amado, ran the group until his death in 1997.

It is now led by five men with close ties to cocaine producers in Colombia, including Juan Jose Esparragoza, also known as ``El Azul,'' Santiago Vasconcelos said.

He said the most powerful of those are Joaquin ``El Chapo'' Guzman and Ismael Zambada, alias ``El Mayo.'' Guzman himself had escaped from a similar top security prison near Guadalajara in 2001.

In November, U.S. authorities offered a $5 million reward for Esparragoza's capture. About a month later, they announced a similar reward for information leading to the apprehension of Guzman. Zambada has been a wanted U.S. fugitive with a $2 million price on his head since 2003.

On Dec. 31, a fellow inmate at La Palma shot and killed Guzman's brother, Arturo, who was held there. Another associate of Guzman had been shot to death inside La Palma on Oct. 6.

The head of Mexico's federal prison guard force, Carlos Tornero, said earlier this month that either guards or trusted suppliers must have been corrupted to allow the guns into the prison. That was especially alarming because the La Palma guards were supposed to be an honest elite force.

Tornero said there would be ``complete and absolute'' changes in the prison administration.

Federal Attorney General Rafael Macedo de la Concha had said last year that officials were investigating reports of an escape plot at La Palma and he acknowledged the problems of holding wealthy, ruthless and powerful drug bosses.

``Some inmates, because of the economic power and organizational strength of their gangs, put prisons under a great deal of pressure,'' Macedo de la Concha said.