Some 40,000 troops are battling the drug gangs nationwide

Two undercover Mexican agents have been killed, apparently by hit-men working for the country's most wanted man, local media reports say.

The agents' bodies were found bound and blindfolded in Durango state, said to be the hiding place of alleged drug cartel head Joaquin "El Chapo" Guzman.

"Neither priests nor rulers will ever get El Chapo," read a chilling note left with the corpses.

The Mexican government has denied it knows where the fugitive Mr Guzman is.

But the note's reference to "priests" is seen as a reference to the Archbishop of Durango.

He caused a major stir, says the BBC's Stephen Gibbs in Mexico City, by declaring two days ago that "everybody knows" that Mr Guzman - who escaped from a maximum security jail in 2001 - was living in the state.

The note may represent a major change in the drugs war in Mexico which has seen 8,000 people killed in the past two years as drug gangs fight for territory amid government crackdowns.

It was thought that there were two institutions that Mexican drug traffickers would rather not confront - the army and the church, our correspondent says.

Now it seems that nothing is off limits, he adds.

Last month, Mexico's attorney general offered a reward of $2m (£1.37m) to informers who help arrest any of the country's 24 most-wanted drug gang chiefs.