KUALA LUMPUR (March 9): Malaysia will not cut diplomatic ties with North Korea while pursuing its investigation of the Kuala Lumpur airport murder, Prime Minister Najib Razak said on Thursday, as North Korea let two Malaysian U.N. employees to leave despite its travel ban.

North Korea had barred Malaysians from leaving the country on Tuesday, sparking tit-for-tat action by Malaysia, as diplomatic tensions escalated over an investigation into the murder last month of Kim Jong Nam, the estranged half-brother of North Korean leader Kim Jong Un.

After initially accusing North Korea of assassinating Kim Jong Nam with a banned chemical weapon and of treating Malaysians like hostages, Najib has struck a more conciliatory tone to help negotiations to get his citizens out of the secretive, nuclear-armed state.

"Diplomatic relations between Malaysia and North Korea will not be severed, as we need to continue communicating with them to find a solution," Najib said in a statement on his blog.

But, he added that his government "will not relent from a firm approach" in dealings with North Korea.

The departure of two Malaysians working for the U.N.'s World Food Programme meant nine still remained at the embassy in Pyongyang. They included three diplomats and six family members.

"The government of North Korea has given a guarantee of safety," Najib said in a message on social network Twitter. "They are free to do their daily activities, but they cannot leave the country."

Najib Razak confirmed on Twitter that the two WFP staffers, Stella Lim and Nyanaprakash Muniandy, had left North Korea and reached Beijing.

It was unclear why the pair, who according to a Malaysian government official held U.N. passports, had been allowed to go.

Najib said he had spoken by telephone to Mohd Nor Azrin, the counsellor at Malaysian embassy in Pyongyang.

"Thank god he, his family and the other Malaysians are safe," Najib said on Twitter.