questions over the effectiveness of the restrictions, as North Korea is still able to trade internationally.

The country's commerce with China, its main ally, was partially responsible for an estimated economic growth of 3.9% last year, Bloomberg news agency reports.

How is the world responding?

The issue of North Korea's weapons programme is expected to dominate US President Donald Trump's address at the UN General Assembly and his meetings with the leaders of South Korea and Japan.

Mr Trump previously warned that "all options" were on the table and that North Korea would face "fire and fury" if it continued to threaten the US.

Media playback is unsupported on your device Media caption Trump is to make his debut at the UN General Assembly: Will he listen or lecture?

In a phone call onMonday, Mr Trump and Chinese President Xi Jinping committed to "maximising pressure on North Korea through vigorous enforcement" of UN Security Council resolutions, the White House said.

Washington has repeatedly urged Beijing to take more direct action to rein in Pyongyang, while China says the US should refrain from issuing more threats.

Russia has also criticised what it describes as "aggressive rhetoric" from the US.

China and Russia only agreed to the new UN sanctions after they were softened by Washington.

Meeting on the sidelines of UN General Assembly, the foreign ministers of both countries reaffirmed their call that the crisis should be resolved by diplomacy, a statement from Russia's foreign ministry said.

What about US-South Korea military drills?

The US military carried out an aerial military drill on Monday with South Korea near