The United States has designated the radical Islamist Syrian rebel group Jabhat al-Nusra, which is suspected of ties to al Qaeda, as a foreign terrorist organization.
In an order released on Tuesday, the U.S. State Department essentially classified the group, which has advocated for an Islamic state in Syria, as an affiliate of al Qaeda in Iraq.
By blacklisting al-Nusra, authorities now can freeze any assets the group or its members have in U.S. jurisdictions. The designation also prohibits Americans from giving it any material support.
The group has been accused by other rebel factions of indiscriminate tactics in the bloody civil war aimed at ousting President Bashar al-Assad.
"The secretary of state concludes that there is a sufficient factual basis to find that al-Qaeda in Iraq ... uses or has used additional aliases," including Jabhat al-Nusra, the State Department statement said.
Tuesday's action comes as U.S. officials attend the Friends of Syria meeting in Marrakesh, Morocco, to discuss the 20-month-old crisis in Syria as rebels push forward on the battlefield and move to unify the political opposition.
U.S. officials have stressed their concern about the rising influence of extremist elements in the Syrian war.
Secretary of State Hillary Clinton had been expected to attend before falling ill with a stomach virus. Deputy Secretary of State Bill Burns is attending in her place.