(Adds background, details)

WASHINGTON, May 13 (Reuters) - The U.S. Treasury Department on Friday sanctioned Aguila Saleh, the president of Libya's internationally recognized parliament in Tobruk, over what U.S. officials say is his blocking of the formation of a U.N.-backed government of national accord.

Saleh "is responsible for stalling political progress in Libya. Today's action sends a clear message that the U.S. Government will continue to target those who undermine the peace, security, and stability of Libya," said John E. Smith, Acting OFAC Director.

The Treasury Department's action means that "all property and interests in property of Issa that are within the jurisdiction of the United States or in the control of U.S. persons are blocked". It added Americans were "generally prohibited" from carrying out transactions with him.

The statement said Saleh had repeatedly blocked votes by Libya's House of Representatives to support the North African country's political transition.

Libya has been in turmoil since the Western-backed uprising that overthrew Muammar Gaddafi five years ago.

Two competing governments, one in Tripoli and the one in Tobruk, backed by armed factions, have struggled for control of the OPEC state since 2014.

A U.N.-backed unity government, designed to replace the rival administrations, arrived in Tripoli earlier this year and is attempting to assert authority over the whole country.

The Treasury Department move follows a similar taken by the European Union in April against Saleh.

Along with Saleh, the EU in April sanctioned Nouri Abusahmain, president of Libya's General National Congress in Tripoli and Khalifa al-Ghwell, prime minister of the self-proclaimed Tripoli government.

The EU said the three played a central role in obstructing the establishment of a unity government in Libya, which has become the main conduit for refugees from North Africa and sub-Saharan Africa to leave in boats for Europe.

(Writing by Yara Bayoumy and Jonathan Landay; Editing by Bernadette Baum and Alistair Bell) ((yara.bayoumy@thomsonreuters.com; tel: +1202 779 1681; Twitter: @yarabayoumy; Reuters Messaging: yara.bayoumy.thomsonreuters.com@reuters.net))

Keywords: LIBYA SANCTIONS/USA