The Russian Foreign Ministry on Tuesday expressed "deep regret" that the Thai government has yielded to external political pressure and illegally extradited the allegedly arms dealer Viktor Bout.

A statement published on the ministry website said the extradition of Bout to the United States was "undoubtedly" a result of "unprecedented political pressure" from Washington on the government and judicial authorities of Thailand.

"This is nothing else like intrusion into law procedures. This makes questionable the independence of the Thai judicial system and decisions made by Thai authorities," said the ministry.

The extradition of the acquitted person has been "irrational, unexplainable and unjustified," it said.

The ministry also said Bout's extradition from Thailand has no legal justification, and Moscow would continue to protect his rights.

Bout was accused of arms trafficking and terrorism by the United States. He was arrested in Bangkok in March 2008 by a U.S. warrant. The Thai court has acquitted Bout twice over lack of evidence.