KUALA LUMPUR, Malaysia — Malaysian authorities are seeking seven more people in the assassination of the half brother of North Korea’s leader, including four North Koreans who left the country shortly after the killing, a top police official said Sunday.

The announcement came as South Korea publicly accused North Korea of responsibility for killing Kim Jong Nam, the estranged elder brother of Kim Jong Un, North Korea’s supreme leader.

At least 11 people, six of them North Korean, have been linked to the plot to kill Kim, a high-level target whose death Feb. 13 in a heavily trafficked area at Kuala Lumpur International Airport has drawn international scrutiny.

According to preliminary reports, Kim was killed by two women who poisoned him, but officials are looking into a wider plot.

Noor Rashid Ibrahim, Malaysia’s deputy inspector-general of police, said at a news conference in Kuala Lumpur that it was a “sudden and suspicious death’’ but that the cause had yet to be determined.

He declined to confirm that the victim was Kim Jong Nam, who was using a passport with the name Kim Chol, though the context was clear.

In Seoul, the South Korean government said that there was no doubt Kim Jong Nam was the victim and that it believed North Korea was responsible.

“Given various information we have and the circumstances, our government is certain that the man murdered was Kim Jong Nam,’’ said Jeong Joon-hee, a spokesman for the South’s Unification Ministry. “Given that there are five suspects from North Korea, we believe that the North Korean regime masterminded the incident,’’ he said.

Jeong said North Korea had a history of committing “crimes against humanity and terrorist acts.’’ He added: “Our country and the international community are watching this reckless and atrocious incident closely and with grave concern.’’

Jeong’s statement marked the first time South Korea has publicly blamed the north for the death. Speaking to lawmakers behind closed doors last week, the country’s intelligence chief, Lee Byung-ho, said that his agency suspected North Korean involvement.

Malaysian news accounts said two women had carried out the attack by injecting Kim with a poison or wiping his face with it.

Noor Rashid would not comment on claims that the women thought they were taking part in a prank when they are said to have poisoned Kim at the airport.

In addition to the two women — one from Indonesia and one carrying a Vietnamese passport — the police have arrested a Malaysian man, who is said to be assisting the police, and Ri Jong Chol, 46, a North Korean man who had been living and working in Malaysia.

Noor Rashid identified the four men who fled the country on the day of the attack as North Koreans ranging in age from 33 to 57. They had arrived separately in Malaysia during the two weeks before the killing, he said. None used a diplomatic passport.

Noor Rashid said the police are seeking three other men whose whereabouts are unknown, including a North Korean identified as Ri Ji U, 30, also known as James.