Texas ? Wholesale prices of cocaine have risen in more than a dozen major U.S. cities as supplies of the powerful drug have shrunk, including in high-volume markets such as Los Angeles and New York, White House drug czar John Walters said.

But the same federal report that Walters said indicates the short supply also suggests that producers might be stockpiling cocaine in South America or Mexico, perhaps waiting until the time is right to export to the United States.

The scarcity was first noted in a May report by the National Drug Intelligence Center, said Walters, who heads the Office of National Drug Control Policy.

“We’ve had a number of programs and a number of efforts that have done things at a level that we haven’t seen before,” he told The Associated Press on Thursday.

The shortage is likely the result of combined enforcement and eradication efforts in the U.S., Mexico and Colombia, the world’s largest producer of cocaine, said Walters, who met with intelligence officials in El Paso this week.