SEOUL-Satellite imagery indicated on Monday that North Korea had tested a rocket engine, and a senior Pyongyang official called Donald Trump a “heedless and erratic old man”, resuming insults of the U.S. president that had been set aside during a thaw.

The statement carried in state media KCNA by Kim Yong Chol, a ruling party vice chairman who was instrumental in arranging a failed second summit in February, was the strongest salvo yet in a war of words that has rekindled in recent days.

He described Trump as impatient, rebuked him over his own rhetoric and repeated a threat from last week that Pyongyang would dust off its previous insult “dotard” for the U.S. leader.

Tensions have been rising in recent weeks as a year-end deadline approaches set by North Korea for Washington to soften its stance in negotiations. Pyongyang has conducted a series of weapons tests and issued strongly worded statements.

Though Trump regularly exchanged insults with North Korea in the first years of his term, both sides had abandoned personal attacks after Trump met North Korean leader Kim Jong Un in Singapore in 2018.

Those comments indicate Trump is “an old man bereft of patience,” the North Korean official said. “As he is such a heedless and erratic old man, the time when we cannot but call him a ‘dotard’ again may come.”

“We have nothing more to lose.”

North Korea had lauded a “special relationship” between the leaders even as it criticised other U.S. officials and their “gangster-like” demands during deadlocked talks. However, Pyongyang bristled last week after Trump again referred to Kim as “Rocket Man”, a nickname Trump used early in his term.

On Sunday, North Korea carried out what it called a “very important” test at its Sohae satellite launching station, a rocket-testing ground that U.S. and South Korean officials once said Pyongyang had promised to shut down.

Commercial satellite images taken on Saturday by Planet Labs showed vehicles and equipment likely to be used in a rocket engine experiment, said Jeffrey Lewis, the director of the East Asia Nonproliferation Programme at the Middlebury Institute of International Studies in California.

“They are mostly gone on Dec. 8, but the ground appears to have been disturbed by the exhaust from the test,” Lewis said, citing photos captured on Sunday.

Asked on Monday if it had been an engine test, a spokeswoman for South Korea’s defence ministry said site monitoring and detailed analysis were under way with U.S. intelligence authorities.