The United States on Tuesday designated Syrian hardline rebel group Al-Nousra Front as a terrorist organization and imposed sanctions on the group's leaders for their alleged links to al-Qaida.
The U.S. State Department said Al-Nousra Front was responsible for 600 attacks since November 2011, including more than 40 suicide attacks.
"The violent, sectarian vision of Al-Nousra is at odds with the aspirations of the Syrian people, including the overwhelming majority of the Syrian opposition, who seek a free, democratic, and inclusive Syria," according to a U.S. statement.
Syrian President Bashar al-Assad has repeatedly accused "terrorist groups" of inciting the violence in Syria.
The blacklisting blocks the U.S. from providing material support to Al-Nousra Front, which has been one of the more deadly groups fighting against al-Assad's regime.
Al-Nousra Front has claimed responsibility for dozens of suicide and car bombings against government targets across Syria. Members of the radical Islamist group have been described as among the most effective fighters in the conflict.
Some of the fighters have, however, been accused of carrying out indiscriminate attacks against civilians. Last week, the Assyrian Democratic Organization in Syria complained that Al-Nousra insurgents attacked Christian property in northern cities, and called on the opposition to "put an end to undisciplined elements of the rebel group."
The U.S. Treasury Department also imposed sanctions against the two leaders of Al-Nousra Front, Maysar Ali Musa Abdallah al-Juburi and Anas Hasan Khattab.
With this move, any assets they may hold in the United States are blocked and U.S. citizens are barred from doing business with them.
Meanwhile, U.S. Defense Secretary Leon Panetta said Tuesday, citing intelligence reports, that Syria has not taken any new steps in recent days that signal a readiness to use its chemical weapons arsenal.
"We haven't seen anything new indicating any aggressive steps to move forward in that way," Panetta told reporters during a flight to Kuwait.
Panetta said that although he would like to believe that Assad has got the international message not to move forward, the US remains concerned that Syria might resort to using chemical weapons, CBS News reported.
Activists said that an attack on a Syrian village on Tuesday killed or injured around 200 members of Assad's Alawite minority sect, activists said, but it remained unclear who was behind the assault.
Casualty counts varied, but several activists said they could confirm 10 dead. They blamed Assad's forces for the attack, which they said involved the shelling of a house in which at least 200 Alawites were hiding.
The opposition-linked Syrian Observatory for Human Rights said 125 were hurt or killed in a series of explosions that destroyed several houses in the town of Aqrab. There were no reports on Syria's state media.
The opposition Local Coordination Committees reported a toll of 200, but did not specify whether they were Alawites or Sunni Muslims.
Assad belongs to the Alawite sect, an offshoot of Shiite Islam. Most of the opposition rebels are Sunni.
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