The United States promised "concrete steps" against Cambodia and the European Union raised a threat to vital trade preferences, after the Southeast Asian nation's main opposition party was banned ahead of elections.
The Cambodia National Rescue Party (CNRP) was dissolved by the Supreme Court on Thursday at the request of the government of Prime Minister Hun Sen, whose rule of more than three decades faces a major challenge at next year's general election.
The ban on the CNRP followed the arrest of its leader, Kem Sokha, for treason. He is accused of plotting to take power with American help.