(MENAFN- Arab News) Activists on Tuesday urged Myanmar President Thein Sein to "turn his words into action" after the former general promised to free all political prisoners by the end of the year. "I guarantee to you that by the end of this year there will be no prisoners of conscience in Myanmar," Thein Sein said during a visit to London. Pro-democracy campaigners, however, have accused the former junta premier of using a series of headline-grabbing amnesties to win foreign aid and investment. "President Thein Sein is very good at PR but he needs to turn his words into action," said Bo Kyi of the Thailand-based Assistance Association for Political Prisoners (Burma), who estimates there are still more than 150 political prisoners behind bars. He said it would be difficult for the government to keep its promise to release all political detainees as dozens more activists are facing trial, including people arrested for protesting without permission. "For the time being rule of law is very weak. There are still arbitrary arrests and there is no fair trial," Bo Kyi added. The military junta which ruled for decades until 2011 had long denied the existence of political prisoners.