The Obama administration said Thursday it wouldn't challenge state laws in Colorado and Washington that allow recreational marijuana use, in the latest victory for the movement to decriminalize the drug.

The decision clears the way for the states to move ahead in implementing their laws and limits the vulnerability of marijuana dealers there to federal prosecution, so long as they comply with state regulations.

"I must admit, I was expecting a yellow light from the White House. But this light looks a lot more greenish than I had hoped," said Ethan Nadelmann, executive director of the Drug Policy Alliance, which advocates loosening marijuana laws.

Critics said the move would lead to increased marijuana abuse and harm to pot users. "I see it as a tsunami in the works," said Calvina Fay, executive director of the Drug Free America Foundation.

In November, voters in Colorado and Washington made their states the first in the nation to permit the use of recreational marijuana. Those two states, plus 18 others and the District of Columbia, permit it for medicinal purposes.