North Korea has carried out a “very important” test at its Sohae satellite launch site, state media KCNA reported on Sunday, a rocket testing ground that US officials once said North Korea had promised to close.

The reported test comes as a year-end deadline North Korea has imposed nears, warning it could take a “new path” amid stalled denuclearisation talks with the United States.Missile experts said it appeared likely the North Koreans had conducted a static test of a rocket engine, rather than a missile launch.

“If it is indeed a static engine test for a new solid or liquid fuel missile, it is yet another loud signal that the door for diplomacy is quickly slamming, if it isn’t already,” said Vipin Narang, a nuclear affairs expert at the Massachusetts Institute of Technology in the United States.

Tensions have risen ahead of a year-end deadline set by North Korea, which has called on the United States to change its policy of insisting on Pyongyang’s unilateral denuclearisation and demanded relief from punishing sanctions.

On Saturday North Korea’s ambassador to the United Nations said denuclearisation was now off the negotiating table with the United States and lengthy talks with Washington are not needed.