Vicente Fox said on Wednesday that the legal process of handing over traffickers on the US government's list had already begun.

"I am confident and convinced that very soon, and I am talking about weeks, we will start the first extraditions of these leaders," Fox said. "I am sure that will provoke additional violence... They will try to retaliate."

The targets of retaliation "could be judges, could be government officials, but we will be ready".

He did not say who would be extradited first, or how many, but said they "are those who are wanted by American justice, the big bosses".

Fox said the drug gang leaders handed over would have to serve their sentences in US jails.

That marks a policy shift. Until recently under Mexican law, drug traffickers first had to serve out prison sentences in Mexico before being jailed in the US.