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By Yeganeh Torbati

WASHINGTON, Feb 11 (Reuters) - The United States blacklisted three people on Thursday for working for Islamic State, including one of the militant group's most prominent ideologues and a senior oil official.

Turki al-Bin'ali was sanctioned for helping Islamic State recruit foreign fighters, the U.S. Treasury said in a statement.

Bin'ali, 31, appears regularly in Islamic State propaganda videos and authored a frequently cited biography of the group's leader Abu Bakr al-Baghdadi.

Experts say the preacher's writings helped lay the religious legal groundwork for the Islamic State to declare a "caliphate," which it did in Syria and Iraq in 2014. Soon after, Bin'ali issued a treatise that rallied militant Islamists to the cause, and has denounced Islamic State's many Muslim critics. Bahrain revoked Bin'ali's citizenship in 2015.

Treasury said that as early as March 2014, Bin'ali led an Islamic State support network "actively recruiting" Gulf nationals to join them in Syria. A Treasury spokesperson said Thursday's actions were the first U.S. sanctions to target Bin'ali.

The sanctions freeze any U.S. assets the men might have and prohibit Americans from dealing with them.

Another man sanctioned on Thursday was Faysal Ahmad Ali al-Zahrani, from Saudi Arabia, who the Treasury Department said is responsible for Islamic State's oil and gas activities in areas of northeastern Syria.

Zahrani for a time answered directly and transferred funds to top Islamic State financial official Abu Sayyaf, who was killed in a U.S. Special Operations Forces raid last May, Treasury said.

As of January 2015, Zahrani controlled at least five oil fields in Syria, and in six months in 2014 and 2015, sent tens of millions of dollars in oil and gas revenues to Islamic State, the Treasury Department said.

The United States has used air strikes and sanctions to cut off the flow of funds to Islamic State, which is estimated to earn hundreds of millions of dollars a year from illicit oil sales, taxation, sales of antiquities, and other methods.

A U.S. Treasury official said this week that the air strikes, which have targeted Islamic State's oil facilities in eastern Syria, have helped to force the group to cut its fighters' pay by up to 50 percent.

Husayn Juaythini, born in a refugee camp in Gaza, was also sanctioned and was trying to establish a foothold for Islamic State in Gaza, the Treasury said.

(Reporting by Yeganeh Torbati; Editing by Alistair Bell) ((Yeganeh.Torbati@thomsonreuters.com; +1-202-445-7940;))

Keywords: USA ISLAMICSTATE/SANCTIONS