British Prime Minister David Cameron (L) greets Myanmar President Thein Sein at 10 Downing Street in central London on July 15, 2013. (AFP/ANDREW COWIE) By Andrew Osborn Reuters: July 15, 2013 LONDON (Reuters) - President Thein Sein, the first leader of Myanmar to visit Britain in more than 25 years, held talks with Prime Minister David Cameron on Monday as activists protested against the Asian nation's human rights record. Sein said in a statement released on his website on Sunday that he had disbanded a security force accused of rights violations against Rohingya Muslims in Rakhine State in the west of Myanmar, scene of deadly violence between Muslims and majority Buddhists in the past year. Sein was due to talk trade, aid and democracy with Cameron and his ministers during a two-day visit at a time when Myanmar is opening up its oil, gas and telecoms sectors to foreign investors, with further liberalisation likely. Cameron was under pressure to confron