BEIJING - The value of China's coal imports from North Korea surged nearly 40 percent in February, official data shows -- the same month Beijing vowed to suspend the trade over Pyongyang's nuclear and missile tests.

China imported $97.6 million worth of North Korean coal last month -- a key foreign currency-earner for the pariah state -- up from $70.1 million during the same period last year, according to China's customs website. Its total imports from the North rose to $176.7 million in the month, up 47 percent from $119.9 million a year earlier. The volume of coal imported last month, however, fell to 1.23 million tonnes from a year-ago 1.52 million tonnes. The data came after Beijing announced on February 18 that it was halting all imports of coal from North Korea for the rest of the year. The move followed another rocket launch by Pyongyang and the assassination in Malaysia of the half-brother of the North's leader Kim Jong-Un.

It is not clear if the Chinese customs data only cover the period before the official suspension came into force or the entire month. China is the North's sole major ally and its economic lifeline, but has come under pressure to do more to rein in its neighbour.

US President Donald Trump has repeatedly accused Beijing of failing to use its leverage to help stop the North's nuclear programme. "North Korea is behaving very badly. They have been 'playing' the United States for years. China has done little to help!" Trump wrote in a Twitter-blast earlier this month.

The hardened US stance followed two North Korean nuclear tests last year and recent missile launches that Pyongyang described as practise for an attack on US bases in Japan. Pyongyang is barred under UN resolutions from carrying out ballistic missile launches or nuclear tests.

Beijing is reluctant to squeeze the unpredictable North too hard lest it trigger a confrontation or messy regime collapse. China wants to resume multi-lateral diplomatic negotiations with North Korea on dismantling its nukes -- which UN resolutions bar it from having -- but various rounds of such talks in years past failed to deter Pyongyang.

Chinese authorities traditionally ensured that UN Security Council resolutions on sanctions against Pyongyang included humanitarian exemptions, and had continued to purchase huge amounts of North Korean coal. But the latest resolution, passed in December, had no such clause and Beijing suspended purchases of coal from the North -- for three weeks to December 31.