A Republican senator has blocked an effort to confirm President Barack Obama's nominee for a key Treasury post responsible for leading the battle against terrorism and financial crimes.

Sen. Tom Cotton of Arkansas objected on Wednesday when Democratic Sen. Sherrod Brown of Ohio tried to move ahead on the long-stalled nomination of Adam Szubin.

Cotton cited the possibility that the Obama administration would ease financial restrictions that prohibit U.S. dollars from being used in transactions with Iran.

Szubin, who was nominated a year ago, has served under both Obama and predecessor George W. Bush. He has been in the anti-terror job in an acting capacity.

Brown criticized Republicans, saying they were holding the government's national security apparatus hostage for politics.