Hundreds of Myanmar villagers have fled to Thailand after government troops raided the stronghold of the Karen National Union, the country's largest rebel group, the Thai army said on Wednesday. "We estimate about 500 villagers have fled Myanmar to seek safe refuge in Thailand after clashes between the KNU and the government on Tuesday," said army spokesman Acra Tiprote. KNU officials said Myanmar troops started bombarding their base about 20 km (12 miles) from the Thai border town of Umpang on Tuesday, the first clash since a ceasefire 13 months ago. Rebels had retrieved the bodies of 12 government soldiers, they said, but gave no details of their own casualties. "They used 200 prisoners as porters," KNU spokesman Tha Na Cee told Reuters from the Union's base. "Several of them, mostly aged between 14 and 17, have surrendered and said they don't want to go back." The KNU agreed to stop fighting in December 2003 but never signed a ceasefire deal.