The US State Department has blacklisted the outfit Ansar al Shari'a, which it said was a "new alias" of the al Qaeda in the Arabian Peninsula (AQAP).
The move bars American citizens from doing business with or providing support to the group, and freezes all of its assets under US jurisdiction, Xinhua reported.
A UN sanctions committee also added the outfit to its list Thursday, a move that subjects the group to a worldwide assets freeze, a travel ban and an arms embargo, the department said.
The outfit, based in Yemen as the AQAP, was established to attract potential followers to the Islamic Sharia rule in areas under its control, the department said.
The Ansar al Shari'a was "simply AQAP's effort to rebrand itself, with the aim of manipulating people to join AQAP's terrorist cause", the department said in a statement.
It said the group has taken responsibility for multiple attacks against Yemeni forces, including a suicide bombing in May, which killed more than 100 Yemeni soldiers.
The Ansar al-Shari'a also launched a series of attacks in Yemen in March, also killing around 100 people, many of them Yemeni soldiers, the department added.
The AQAP was branded by Washington as a foreign terrorist organisation in January 2010, as the group was accused of trying to bomb American and Western interests time and again.
"We are determined to eliminate AQAP's ability to execute violent attacks and to disrupt, dismantle and defeat their networks," the State Department said.