By Lesley Wroughton and Mark Hosenball WASHINGTON (Reuters) – The United States is pressing Cuba to allow the opening of its embassy in Havana by April, U.S. officials told Reuters, despite the Communist island’s demand that it first be removed from the U.S. list of state sponsors of terrorism. A refusal by Cuba to allow the United States to quickly establish an official embassy for the first time in half a century could complicate talks between the Cold War foes, reflecting enduring mistrust as they move to end decades of confrontation. It would also mark the first major setback since President Barack Obama’s historic shift in Cuba policy in December, suggesting one of the biggest foreign policy moves of his administration is struggling to achieve even its first goal.