The head of the U.S. congressional panel on foreign affairs has lodged a strong protest with the Chinese government against its recent repatriation of nine North Korean defectors, his office said Friday.

Rep. Ed Royce (R-CA), chairman of the House Foreign Affairs Committee, sent a letter to China's President Xi Jinping expressing his concern over recent reports of the forced repatriation of nine North Korean defectors, some as young as 15, who now face extreme punishment in North Korea, including torture and execution, his office said in a press release.

"The U.S. and China must work together to address the serious challenges that North Korea poses to the world community. I strongly encourage the Government of the People's Republic of China to work closely with the U.S. and others to find an alternative to forced repatriations," Royce wrote in the letter.

The statement came as U.S. President Barack Obama plans to meet Xi in California next week.

The nine North Koreans -- reportedly between age 15 and 23 -- fled North Korea in 2011 and were hiding in China. They then moved to Laos in hopes of settling in South Korea.

They were caught by the Lao authorities and earlier this month deported to China, which later repatriated them to the North.

The Obama administration said it was not directly involved in the case, although it said it is keeping close tabs on related events.

"We are very concerned about the reports we have seen that the individuals have been sent back to North Korea," State Department spokeswoman Jennifer Psaki said at a press briefing. "We urge all countries in the region to cooperate in the protection of North Korean refugees within their  territories. We do remain very concerned about their well-being and we're monitoring it closely."

Some human rights groups here said they would hold protest rallies in front of the embassies of China and Laos.

Dennis Halpin, a Korea expert in the U.S., also accused the Lao authorities of breaking a "gentlemen's agreement."

"The news from Laos of the recent repatriation was especially disturbing. It seemed a break with long-term, unofficial arrangements under which Lao officials looked the other way with regards to North Korean refugees. It is a major blow to the underground refugee network," said Halpin, a long-time congressional staffer and currently a visiting scholar at the U.S.-Korea Institute at Johns Hopkins University.

He said bribes from Pyongyang might have led Laos to abandon its longstanding policy of cooperating with South Korea on the issue of North Korean refugees.

"Certainly not by coincidence, a Lao delegation was recently in Pyongyang," he said in an op-ed piece on the website for the Center for Strategic and International Studies. "How much blood money did (North Korean leader) Kim Jong-un pledge in return for the forced repatriation of refugees? Did this lead the Lao to renege on the 'gentlemen's agreement' on North Korean refugees which they had previously reached with the South Korean Embassy in Vientiane?" (Yonhap News)