By Oleg Vukmanovic MILAN (Reuters) - Angola's liquefied natural gas (LNG) export plant is experiencing fresh delays in raising production and shipping a cargo, according to trade sources. The plant, shut since April 2014 following construction errors and difficulty in handling feed gas supplies, began the process of re-starting in January, a spokesman for the Chevron-led venture said at the time. A spokesman for Angola LNG declined to comment this week on the timing of production operations. Trade sources told Reuters that Angola LNG had told them to expect the first cargo to load on May 15, which was to be followed by a supply tender in June. Both have now been postponed, they said. The plant is expected to start-up production operations at the end of May and a first cargo should be shipped in June, one source close to the matter said. The Sonangol Sambizanga LNG tanker, currently moored at one Angola LNG jetty, is only conducting tests, not loading supply, the source added. After producing a limited number of cargoes, Angola LNG will then be shut down again for additional testing, sources said. Traders had initially expected the plant to produce and export a cargo in April. Chevron has a 36.4 percent share in the plant, while Angolan state oil firm Sonangol has 22.8 percent. Other stakeholders include Total, BP and ENI. (Additional reporting by Sarah McFarlane in London, editing by William Hardy)