North Korean leader Kim Jong-il has pledged to develop his country's friendship and cooperation with China.

On the 57th anniversary of the People's Republic of China Saturday, the North's Korean Central News Agency said Kim sent a congratulatory letter to Chinese President Hu Jintao.

The letter said Pyongyang's Workers' Party and government wants to develop bilateral relations.

The move comes as relations between the two communist allies have chilled since the North's test launches of missiles in early July.

China also approved a U.S.-led campaign to impose sanctions against the North, and Kim recently said China cannot be trusted.

The letter was also signed by the North's parliamentary leader Kim Yong-nam and Cabinet Premier Pak Pong-ju.