By Chen Aizhu and Oksana Kobzeva SINGAPORE/MOSCOW (Reuters) -U.S. sanctions pose a major obstacle to Russia’s plans to increase exports of seaborne liquefied natural gas (LNG) to offset the decline in pipeline gas exports to Europe, analysts said, as expectations mount of delays to a flagship project. The world’s fourth largest LNG producer after the United States, Qatar and Australia, Russia has an ambition to increase its share of the global market to around a fifth from 8% now by tripling its output to more than 100 million metric tons by 2030-35. But whereas Moscow has successfully diverte…