(CNN) -- The U.S. Treasury imposed sanctions Tuesday on leaders of the jihadist al-Nusra Front in Syria, hours after the State Department moved to blacklist the rebel group as a foreign terror organization linked to al Qaeda in Iraq.

The Treasury also sanctioned two armed militia groups that operate under the control of the Syrian government, Jaysh al-Sha'bi and Shabiha, it said.

Syrian opposition groups have voiced their opposition to the U.S. move against the rebel fighters, suggesting that they are being targeted because they oppose a new anti-government coalition.

In recent months, the radical Islamist al-Nusra Front has emerged as one of the most effective groups in the Syrian resistance, drawing on foreign fighters with combat experience in Iraq and elsewhere.