MONTERREY, Mexico, (Reuters) – Washington is closely  watching Mexico’s recent decriminalization of drugs but  respects its neighbour’s move as a tool in the fight against  drug cartels, two senior U.S. officials said yesterday.

Mexican President Felipe Calderon last month signed a law  legalizing possession of small amounts of marijuana, heroin,  opium, cocaine, methamphetamine and LSD for personal use, three  years after the country ditched a similar plan under pressure  from the Bush administration.

More than 13,000 people have died in Mexico’s drug war  since late 2006. The escalating conflict appears to have nudged  the United States, now under the Obama administration, toward  quiet support despite its own prohibitionist federal laws.

“We will take a watchful attitude. It is clearly in the  authority of the government of Mexico to pass these laws,” U.S.  drug czar Gil Kerlikowske told Reuters during a visit of border  governors to the northern Mexican city of Monterrey.

Mexico says the new law frees it up to go after major  criminal cartels that move billions of dollars of narcotics  into the United States, the world’s top illicit drug market.

Crushing the cartels, who arm themselves with weapons  smuggled from the United States and kill rivals at will on busy  city streets, has become a major test of Calderon’s presidency  as the violence worries investors.

Hooded gunmen burst into a Mexican rehabilitation clinic  near the U.S. border on Wednesday, lining up patients before  killing 17 of them.

“President Calderon has taken on (the drug cartels) …  using limited law enforcement resources, including the  expansion of laws to go after drug dealers, using tools that he  didn’t have, and that is something that the Obama  administration applauds,” U.S. border czar Alan Bersin said.

The support appears to mark a change in Washington’s  approach to the drug war.