Greece and Cyprus say their delegations left a U.S.-hosted nonproliferation conference over objections about how Macedonia was represented.
The two countries' embassies say their delegations left after learning that Macedonia would be identified as the Republic of Macedonia, the name recognized by the United States.
Athens argues the name implies a territorial claim against the northern Greek province of Macedonia. Cyprus supports Greece's objection.
The Greek Embassy says that it made clear that it would not participate in international meetings in which Macedonia is not referred to as FYROM. FYROM stands for the Former Yugoslav Republic of Macedonia and is name used in the United Nations.
Greece recently blocked Macedonia's bid to join NATO over the issue.