The United States says it has blocked military aid to Rwanda for backing M23 rebels, who are active in the east of the Democratic Republic of Congo and use child soldiers in their fight against Kinshasa.

The US State Department said on Thursday that the sanctions also apply to the Central African Republic, Myanmar, Sudan and Syria.

Washington has been strengthening the military of Rwanda -- a staunch ally in Africa -- for decades despite Kigali’s blatant interference in neighboring Congo, but other nations reportedly do not receive any military aid from the US.

"Our goal is to work with countries who have been listed to ensure that any involvement in child soldiers -- any involvement in the recruitment of child soldiers -- stop," US Assistant Secretary of State for African Affairs Linda Thomas-Greenfield said.

State Department spokeswoman Marie Harf said Rwanda was sanctioned because of its "support for the M23, a rebel group which continues to actively recruit and abduct children" and to threaten the stability of Congo.

The March 23 movement (M23) rebels defected from the Congolese army in April 2012 in protest over alleged mistreatment in the army.

The UN and Kinshasa have repeatedly accused Rwanda of helping the rebels in Congo. Rwanda has always denied the charges that it is backing the M23, but Kigali has never publicly condemned the militia, which is strengthening its grip over the provinces of North Kivu and South Kivu in the eastern Congo.

Military spokesman Brigadier General Joseph Nzabamwita said that Rwanda is not responsible for events in Congo.

"It is surprising that Rwanda would be liable for matters that are neither on its territory, nor in its practices," he said. "As a long term partner of the Rwanda Defense Forces, the United States has ample evidence that our forces have never tolerated the use of children in combat."

"Rwanda's commitment to a sustainable solution that seeks to bring an end to the DRC conflict and its consequences, including the use of child soldiers, remains unchanged," Nzabamwita added.

"The collaboration between the Government of Rwanda and the United States remains strong, particularly in the field of peacekeeping, and Rwanda will continue to hold its forces to the highest standards of professionalism and discipline," he noted.

The M23 rebels and several other armed groups are active in the eastern Congo and are fighting for control of the country’s vast mineral resources, such as gold, the main tin ore cassiterite, and coltan (columbite-tantalite), which is used to make many electronic devices, including cell phones.

Since early May 2012, nearly three million people have fled their homes in the eastern Congo. About 2.5 million have resettled in Congo, but about 500,000 have crossed into neighboring Rwanda and Uganda.

The eastern Congo has experienced interminable cycles of violence since 1998.

The war in the Congo has dragged on for over a decade and left over 5.5 million people dead.