A young man who disrupted the Nobel prize ceremony in Oslo by waving a Mexican flag streaked with red said Thursday he did it to denounce the alleged killing of students by Mexican authorities.

The protest by the 21-year-old at the presumed massacre of 43 Mexican students came as Pakistan's Malala Yousafzai and India's Kailash Satyarthi displayed their peace prizes to rapturous applause on Wednesday.

The security breach was especially serious since child rights activist Malala, who was lucky to survive a Taliban assassination attempt in October 2012, remains a target for Islamist extremists.

The Mexican protester, Adan Cortes Salas, said he was sorry for having frightened anyone and for any repercussions the security services may face, but did not regret his actions.

"My message was... 'help to Mexico'," Salas told NRK television in Norway during an interview conducted in a detention centre. "Our government is killing students."

Salas, a student and asylum seeker who entered Norway in late November, said he simply dressed well and walked into the ceremony at Oslo city hall as if he belonged there.

He wore glasses and a camera around his neck, and held the Mexican flag as he approached the two laureates on stage. He said he asked them for an opportunity to speak on the microphone.

He was grabbed by security agents shortly afterwards and escorted away. He has since agreed to pay a fine of 15,000 krone ($2,000, 1,700 euros) and has been handed over to immigration police.

Salas told VG newspaper that his actions had not been planned for very long, saying he found out the ceremony was occurring while he was in town and decided on the protest.

Police have apologised over the incident, with Oslo police chief John Fredriksen saying "it shouldn't have happened."

Mexican media said he was a left-wing militant who wanted to draw the world's attention to the disappearance of 43 students in southern Mexico caught up in the country's bloody drug war.

Prosecutors have confirmed that one of the missing students was among charred remains found in a landfill and nearby river in Guerrero state.

The identification by an Austrian medical university bolstered suspicions that the students were slaughtered by a drug gang after they were delivered to hitmen by corrupt police.

The two Nobel laureates appeared unperturbed by the protest at the ceremony.

"There was nothing to be scared of," Malala said in a press conference Thursday.

"There are problems in Mexico, there are problems even in America, even in Norway. So the problems are always there in every country and it's really important that children raise their voice, children come forward," she added.