The United States said on Friday it was deeply concerned by the detention of a U.S. citizen who was working as a journalist in Myanmar and pressed the military government for his immediate release. A spokesperson for the U.S. State Department said consular officers from the U.S. Embassy in Yangon had sought to visit the journalist, Daniel Fenster, but had not been allowed access. Fenster, managing editor of Frontier Myanmar, one of the country"s top independent news sites, was detained at the main international gateway in Yangon on Monday while preparing to fly to Malaysia, the publication said this week. read more Frontier Myanmar said on Monday that Fenster, 37, had been transferred to Yangon"s Insein Prison. It said it did not know why he had been detained and had not been able to contact him. The State Department called Fenster"s detention and the arrest and use of violence by the Myanmar military against other journalists an "unacceptable attack on freedom of expression." "We are deeply concerned over the detention," the spokesperson said. "We have pressed the military regime to release him immediately and will continue to do so until he is allowed to return home safely to his family. "We urge the Burmese regime to grant consular access, as required by the Vienna Convention on Consular Relations, without delay, and to ensure proper treatment of Daniel while he remains detained." Myanmar has been in turmoil since the military overthrew the elected government on Feb. 1, citing alleged election fraud. The intervention sparked protests and strikes that the military has struggled to suppress, despite its use of lethal force and the arrest of thousands of people. Journalists have been among those held, accused of incitement by the junta, which has restricted internet access, banned satellite broadcasts and rescinded the licenses of several news organizations. The United States, the European Union and others have responded with economic sanctions, but the junta has shown no sign of compromise. U.S. Deputy Secretary of State Wendy Sherman will visit Southeast Asia next week, including Myanmar"s neighbor Thailand, and plans to discuss the Myanmar crisis while there.