TEHRAN -- President Mahmoud Ahmadinejad accused Britain yesterday of being behind weekend bombings that killed five people in Iran. His comments reflected sharply escalating tension with the West, after the United States and Britain asserted last week that Iran had been involved in insurgent attacks in neighboring Iraq. ''We are very suspicious about the role of British forces in perpetrating such terrorist acts," the student news agency ISNA quoted Ahmadinejad as saying in reference to the two bombings Saturday in southwestern Iran.