China has urged Kuala Lumpur to continue its investigation of Malaysia Airlines Flight MH370, even as relatives of passengers of the missing plane protested outside the airline's office in Beijing. Malaysian Prime Minister Najib Razak announced Thursday that a piece of aircraft debris, found last week on Reunion Island in the Indian Ocean, was confirmed to be from Flight MH370.

Hua Chunying, the spokeswoman for China’s foreign ministry, told Malaysia to "earnestly safeguard the legitimate rights and interests" of the victims' families, Reuters reported, citing the ministry’s website.

Australian Prime Minister Tony Abbott also said Thursday that the "baffling mystery" of Flight MH370, which went missing in March 2014, is a step closer to being solved, according to BBC, adding that the Australia-led search for the plane will continue as "we owe it to the hundreds of millions of people who use our skies."

The confirmation about the origin of the debris came jointly from French authorities, the Bureau d’ Enquetes et d‘ Analyses pour la Securites de I’AviationCivile (BEA), the Malaysian investigation team, and representatives from China and the Australian Transportation Safety Bureau (ATSB), Malaysia Airlines said in a statement Thursday. 

The latest findings, however, unleashed a fresh round of criticism about the long-running investigation and its handling by various authorities.

A dozen relatives of Chinese passengers on the plane gathered Thursday outside Malaysia Airlines' office in Beijing to stage protests against the airline's handling of the investigation, according to the Associated Press, holding signs reading "Malaysia hides the truth," and another that called on Chinese President Xi Jinping for help.

“I’m so angry, I can’t control myself,” Xu Jinghong, whose mother was on board Flight MH370, said, according to the Wall Street Journal, adding: “I can’t believe what they’ve said…I don’t know what the proof is and they haven’t told us.”

Xu said that she first heard about the confirmation of the debris' link to Flight MH370 on a family WeChat group, and claimed that the airline did not call her about the news. 

“What other evidence do you have? Show me something persuasive. As family members, to be subjected daily to misleading news, there is no public morality here. It’s too cruel. We are already in pain, our families lost and we are unable to find them,” Xu said, according to the Journal.

Meanwhile, residents of Reunion Island turned over other things, including old shoes, scrap metal, a wallet, a tea kettle, a Frisbee and part of a ladder, to aid the investigation, according to reports, though they have not yet been confirmed to be from the plane.

Malaysia Airlines, in a statement, said that it would like to “sincerely convey our deepest sorrow to the families and friends of the passengers onboard Flight MH370 on the news,” adding: “We expect and hope that there would be more objects to be found which would be able to help resolve this mystery.”

K.S. Narendran, whose wife was on Flight MH370 said, according to CNN: "I was left somewhat confused and, frankly, a little angry and dismayed," adding "I didn't hear facts. I didn't hear the basics. I heard nothing, and so it leaves me wondering whether there is a foregone conclusion, and everybody is racing to the finish."