The United States will ensure that the U.N. Security Council's resolution imposing arms embargo be well observed as concerns about closer military ties between North Korea and Myanmar grow.

U.S. Defense Department spokesman Jeff Morrell said Thursday that Washington is closely watching military cooperation between the two nations as the UNSC resolution bans Pyongyang from exporting its arms and nuclear technology.

The spokesman, however, failed to elaborate on some media reports that Myanmar is being aided by North Korea in developing weapons of mass destruction.

U.S. Senator Jim Webb abruptly canceled a trip to Myanmar Thursday due to new allegations that Myanmar is working with North Korea to develop nuclear weapons.