North Korea and Syria have agreed to strengthen their cooperation in defending their rights to national sovereignty, according to an official media report from Pyongyang on Tuesday, after the United States ratcheted up pressure on those two countries.

"The two friendly countries are celebrating this anniversary and, at the same time, conducting a war against the big powers' wild ambition to subject all countries to their expansionist ... policy," Syrian President Bashar Assad said in a message sent to North Korean leader Kim Jong Un, according to the Korean Central News Agency.

The message, for the 105th anniversary of the birth of Kim's late grandfather and North Korea's founder, Kim Il Sung, noted that the two countries are "as ever struggling for their rights to self-determination and national sovereignty, and the security and prosperity of their countries," KCNA said.