President Donald Trump said on Tuesday that Chinese efforts to persuade North Korea to rein in its nuclear program have failed, ratcheting up the rhetoric over the death of an American student who had been detained by Pyongyang.

Axar.az reports citing Reuters.

Trump has held high hopes for greater cooperation from China to exert influence over North Korea, leaning heavily on Chinese President Xi Jinping for his assistance. The two leaders had a high-profile summit in Florida in April and Trump has frequently praised Xi while resisting criticizing Chinese trade practices.

"While I greatly appreciate the efforts of President Xi & China to help with North Korea, it has not worked out. At least I know China tried!" Trump wrote on Twitter.

It was unclear whether his remark represented a significant shift in his thinking in the U.S. struggle to stop North Korea's nuclear program and its test launching of missiles or a change in U.S. policy toward China.

"I think the president is signaling some frustration," Christopher Hill, a former U.S. ambassador to South Korea, told MSNBC. "He's signaling to others that he understands this isn't working, and he's trying to defend himself, or justify himself, by saying that at least they tried as opposed to others who didn't even try."

On Tuesday, a U.S. official, who did not want to be identified, said U.S. spy satellites had detected movements recently at North Korea's nuclear test site near a tunnel entrance, but it was unclear if these were preparations for a new nuclear test - perhaps to coincide with high-level talks between the United States and China in Washington on Wednesday.

“North Korea remains prepared to conduct a sixth nuclear test at any time when there is an order from leadership but there are no new unusual indications that can be shared,” a South Korean Defense Ministry official said, speaking on the condition of anonymity.

Seoul was in close consultation with Washington over the matter, the official added.

North Korea last tested a nuclear bomb in September, but it has conducted repeated missile test since and vowed to develop a nuclear-tipped missile capable of hitting the U.S. mainland, putting it at the forefront of Trump's security worries.