WASHINGTON (REUTERS/AFP) - The United Nations Security Council must be prepared to impose new sanctions on North Korea amid escalating tensions over its missile and nuclear programs, US President Donald Trump said on Monday (April 24) ahead of a lunch with ambassadors from countries on the UN council.

Trump, speaking to reporters, said the council also failed to act in response to a recent Syrian chemical weapons attack, which he called a "great disappointment".

"The status quo in North Korea is also unacceptable and the council must be prepared to impose additional and stronger sanctions on North Korean nuclear and ballistic missile programs," Trump said.

"This is a real threat to the world, whether we want to talk about it or not. North Korea is a big world problem and it's a problem that we have to finally solve," he said.

Trump also discussed the "urgent security challenge" posed by North Korea with German Chancellor Angela Merkel in a phone call on Monday, the White House said.

A White House statement said the two leaders also discussed Syria and Yemen and the need for a peaceful settlement to the conflict in Ukraine

US defence leaders and other top officials will give a classified briefing on North Korea to all senators in an unusual meeting at the White House, the Pentagon said on Monday.

The briefing will be conducted Wednesday (April 26) by Pentagon chief Jim Mattis, Secretary of State Rex Tillerson, Director of National Intelligence Dan Coats and General Joe Dunford, who is America's top officer and chairman of the Joint Chiefs of Staff.

They "will be briefing all senators on the current strategic situation with regards to North Korea," Pentagon spokesman Navy Captain Jeff Davis said.

While lawmakers often receive classified briefings, these are usually conducted in secure rooms in the Capitol building and not at the White House.

The briefing comes at a time of soaring tensions between Washington and Pyongyang.

An official North Korean website warned Monday that Pyongyang will "wipe out" the United States if Washington starts a war on the peninsula, the latest tit-for-tat saber-rattling between the two countries.

The United States has deployed an aircraft carrier strike group led by the USS Carl Vinson to the western Pacific, and observers say North Korea appears to be readying a sixth nuclear test.

US officials have warned that "all options are on the table" in dealing with the North Korean threat but have so far relied on China to rein in its unpredictable ally.

The United States has 100 senators. It was not immediately known if all of them were expected to attend Wednesday's meeting.