The New York-based watchdog said it had received reports that 200 people seeking refuge from fighting had reached the Thai border, while 3,000 were still making the dangerous journey, often without adequate food.

"The Burmese army is driving thousands toward the border with Thailand and herding villagers into squalid relocation sites or into the jungle away from their ruined homes and dying crops," said Brad Adams, Asia director at Human Rights Watch (HRW). The report comes after the International Committee of the Red Cross was this week ordered to shut down all its five field offices outside Yangon, one of which is in eastern Karen State where the attacks are said to be taking place.

Fighting involving the Karen National Union (KNU), the oldest and largest rebel force still battling the Myanmar's military regime, has escalated since February in the country formally known as Burma.

HRW said that a year-long military offensive against the ethnic minority rebels in Karen state had displaced 27,000 civilians, with at least 45 civilians killed by government forces.