U.S. President Barack Obama on Friday signed an executive order imposing sanctions against Syrian officials and entities, the White House said in a statement.

The White House said the executive order imposed sanctions against Syrian officials and others responsible for "human rights abuses", including the use of "violence against civilians" and the "commission of other human rights abuses."

The U.S. "strongly condemns" the Syrian government's "continued use of violence" and "intimidation" against the Syrian people, said the White House, calling on the Syrian government to refrain from "further acts of violence."

The targeted individuals include Mahir al-Assad, who is the brother of Syrian President Bashar al-Assad and brigade commander in the Syrian Army's 4th Armored Division, Atif Najib, who is the cousin of President al-Assad, also the head of the Political Security Directorate (PSD) for Dar'a Province during March 2011, and Ali Mamluk who is the director of Syria's General Intelligence Directorate (GID).

The targeted entities are the Syrian General Intelligence Directorate (GID) and the Iranian Islamic Revolutionary Guard CorpsQods Force, which is a branch of the Islamic Revolutionary Guard Corps.

"Any property in the United States or in the possession or control of U.S. persons in which the individuals listed in the Annex have an interest is blocked, and U.S. persons are generally prohibited from engaging in transactions with them," the White House added.

The executive order came days after White House spokesman Jay Carney said the U.S. was considering "targeted sanctions" against al-Assad and his inner circle.

Other U.S. sanctions against Syria have been in place for years. The Bush administration initially imposed sanctions on Syria on May 11, 2004, then extended them on April 25, 2006 and expanded them on Feb. 13, 2008 to target some Syrian officials.

Syria has been gripped by months of protests that erupted in a number of cities amid calls for sweeping reforms.

A military source said on Thursday that 78 soldiers and 70 civilians had been killed in Syria since the unrest broke out six weeks ago, Syrian Arab News Agency SANA reported.

The source dismissed allegations made on some satellite TV channels about the withdrawal of some members of the ruling Bath party and also denied reports that 450 people were killed since the unrest erupted, calling it "poison of false propaganda."