Around 200 foreign journalists gathered in Pyongyang for DPRK's biggest national day, the "Day of the Sun," and were taken to what was billed by officials as a "big and important event" early on Thursday.

It turned out to be the opening of a new street in the center of the capital, attended by DPRK leader Kim Jong Un. A series of skyscraper apartment blocks, including the capital's highest building, have risen since construction started last year. 

The DPRK celebrates the 105th  birthday of its founder Kim Il Sung on Saturday. In 2012, it attempted to launch a long-range rocket carrying a satellite to mark the date, and tested a newly developed intermediate-range missile last year.

The DPRK's official Korean Central News Agency (KCNA) reported early on Thursday that Kim had guided a training session, that saw the army's special operation forces jumping from aircraft.

"He said with pleasure that the commanding officers made correct decisions, adding those combatants carrying out their duties independently and pro-actively were reminiscent of fierce tigers crossing the mountain ranges," KCNA reported.

US officials said the country's President Donald Trump was considering tougher sanctions that could possibly include an oil embargo, banning DPRK's airline, intercepting cargo ships, and punishing Chinese banks for doing business with Pyongyang.

"There's a whole host of things that are possible, all the way up to what's essentially a trade quarantine on the country," one official, speaking on condition of anonymity, told Reuters in Washington on Wednesday.

Trump and Chinese President Xi Jinping spoke by telephone on Wednesday, just days after they met in the US for the first time, underscoring the sense of urgency about the DPRK.

Trump said on Twitter his call with Xi was a "very good" discussion of the "menace" of the DPRK. He said later on Wednesday the US was prepared to tackle the crisis without China, if necessary.