German Foreign Minister Sigmar Gabriel on Sunday urged international powers to diplomatically engage with North Korea to end its nuclear and ballistic missile programs.

Speaking in China, a key economic and political ally of Pyongyang, Gabriel called for a dual strategy of "pressure and dialogue" to deal with the isolated communist regime.

The international community must "decisively and completely implement" sanctions on North Korea, while taking "bold steps" to de-escalate tensions on the Korean peninsula, he said alongside Chinese State Councilor Yang Jiechi in Beijing.

For this, the United States, China and Russia will have to sit at the table and negotiate, Gabriel said. "Without cooperation between these three states the problem will not be solved," he remarked.

Read: Why China won't help US against North Korea

US threatens military action

North Korea has pressed on with its nuclear and ballistic missile programs despite multiple international sanctions, including a new round this week that limited oil imports to the regime.

The failure of sanctions to stop North Korea's progress has prompted the United States to threaten military action should diplomacy fail.

"If our diplomatic efforts fail, our military option will be the only option left," US Secretary of State Rex Tillerson said Sunday, a day before the UN General Assembly is to meet in New York, where North Korea is top on the agenda. 

He said the United States would pressure Russia and China to take tougher action to economically isolate North Korea, including by limiting its oil supplies and cutting off laborers in Russia that are a key supply of foreign exchange. 

Read: How North Korea survives on an oil-drip from Russia

US Ambassador to the UN Nikki Haley said in an interview with CNN that UN Security Council sanctions had been "pretty much exhausted."

"If North Korea keeps on with this reckless behavior, if the United States has to defend itself or defend its allies in any way, North Korea will be destroyed. And we all know that. And none of us want that. None of us want war," she said.

Gabriel: Kim Jong Un 'is not crazy'

The comments came as US President Donald Trump spoke by telephone with South Korean President Moon Jae. The White House said the two agreed to "maximize economic and diplomatic pressure on North Korea" as the UN holds its General Assembly this week in New York. Trump, meanwhile, tried his hand at wit by calling Kim "Rocket Man" on Twitter: "I spoke with President Moon of South Korea last night. Asked him how Rocket Man is doing. Long gas lines forming in North Korea. Too bad!" 

Read: North Korea: From war to nuclear weapons

Gabriel said that sanctions would take time to have an effect on North Korea, which last week launched a second ballistic missile over Japan into the Pacific Ocean.

In an interview with Germany's Bild newspaper, Gabriel argued North Korean dictator Kim Jong Un "is not crazy."

"He follows a coldly laid out strategy: When he has an atomic bomb, then he thinks that his regime is secure. Because he knows that nobody would dream of threatening him," Gabriel said.

cw/jm (AFP, dpa)