The United States has blocked a request for the UN Security Council to allow a Libyan navy vessel's return home to combat migrant smuggling, documents obtained by AFP on Thursday showed.The El Hani frigate was taking on water when it was sent to Malta in 2013 to undergo extensive repairs under a contract with Maltese-based Cassar Ship Repair. Ammunition aboard the frigate was stored during the work.Malta told a UN sanctions committee Libya's UN-backed government now wanted the repaired warship returned along with its ammunition as part of Tripoli's effort to combat migrant smuggling. The Libyan government is allowed to import weapons and military hardware with the approval of the UN sanctions committee overseeing the arms embargo imposed on Libya in 2011.Malta proposed last month that the committee agree to the request, given that the ship was once again seaworthy and planned for use as a patrol boat in Libyan waters, "in view of migration and smuggling issues."The US put a hold on the request on August 28 "pending further review," according to a document seen by AFP.The US mission to the United States declined to comment on its decision to block the request. A US official said that "we cannot share details of closed-door negotiations."Sweden, which chairs the Libya sanctions committee, said the request was still being reviewed.In June the Security Council slapped sanctions on six individuals accused of migrant trafficking in Libya after a video showing African migrants being sold as slaves sparked global outrage last year.Libya descended into chaos after the 2011 overthrow and killing of Muammar Gaddafi, with two rival governments scrambling for control of the oil-producing country. Smugglers operating with impunity in Libya have loaded hundreds of thousands of migrants on boats to reach Europe by sea since 2014, and thousands have died during the voyages.* Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERFOLLOW News24 Africa on Twitter and Facebook.