Saudi-owned crude oil supertanker Sirius Star is seen during its naming ceremony in South Korea in this undated handout picture released on June 18, 2008 and obtained by Reuters on Nov. 18, 2008.

WASHINGTON, Nov. 20 (Xinhua) -- The United States imposed on Thursday financial sanctions against three alleged leaders of an extremist Islamic militia in Somalia.

The three targeted by the U.S. Treasury Department are Mukhtar Robow, spokesman for al-Shabaab and a military commander with the group; Ahmed Abdi Aw-Mohamed, alleged founder and leader of al-Shabaab; and Issa Osman Issa who served as a commander in al-Shabaab.

Washington accuses al-Shabaab of having links to the al-Qaida terrorist group and using intimidation and violence to undermine the Somali government and threaten activists working for peace.

Under U.S. law, any banks accounts or other financial assets belonging to the alleged leaders found in the United States must be frozen. Americans also are forbidden from doing business with them.

The U.S. sanctions comes as calls mount to the United Nations to send peacekeepers to Somalia, as well-organized piracy off the east African nation's sprawling coast is rising dramatically in past few weeks.

Eight vessels have been seized in last two weeks, including a massive Saudi supertanker loaded with 100 million U.S. dollars worth of crude oil.