London, April 21, SPA -- An international human rights group has accused the army of Myanmar (Burma) of using chemical weapons in an attack on rebel groups in the country. The incident is alleged to have taken place near Burma's north-western border with Thailand in February, the BBC reported Thursday. The attack left rebel fighters vomiting blood and unable to walk, Christian Solidarity Worldwide said. The group said it had evidence which suggested that chemical weapons were responsible for the men's injuries. According to accounts from Karen rebel fighters, who have been engaged in a long-running war with Burma's military government, the attack took place just inside the Burmese border, around 16 kilometers from the Thai town of Mae Hong Son. They claim that clouds of yellow vapour began pouring from shells fired at their positions and soon after this many of them felt sick, vomited blood and were unable to walk. Some later suffered from blisters and acute diarrhea. The president of Christian Solidarity Worldwide, Australian physician Dr Martin Panter, has since flown to the area and examined five of the men. He concluded that their symptoms were synonymous with exposure to some form of chemical attack. The British Foreign Office said it was "very concerned" about the allegations and will be examining any evidence. --SPA 1105 Local Time 0805 GMT www.spa.gov.sa/256801