Trump team briefs senators on North Korea

US senators have arrived for an extraordinary briefing by the Trump administration on the threat posed by North Korea and US options in dealing with it.

All 100 senators were invited to Wednesday's classified briefing at a building next to the White House. They were ferried from the Capitol by bus.

President Donald Trump's secretary of state, defence secretary, top general and national intelligence director will brief them. The briefing team was to speak later to House members in the Capitol.

Though highly unusual, the briefings do not necessarily reflect a security crisis is imminent, although military tensions are rising on the divided Korean Peninsula.

But alarm is rising over North Korea's progress in developing a nuclear-tipped missile that could strike America.