UN Secretary-General Antonio Guterres said Wednesday the conflict in Libya has entered a "new phase" due to increased foreign interference in the country.

"The conflict has entered a new phase, with foreign interference reaching unprecedented levels, including in the delivery of sophisticated equipment and the number of mercenaries involved in the fighting," Guterres told the UN Security Council through video-conference.

"Time is not on our side in Libya," he warned and urged the international community to use every opportunity to unblock the political dead-end.

Although noting that the situation on the frontlines has mostly been quiet since 10 June, with UN-recognised Government of National Accord (GNA) forces 25 kms from the Mediterranean coastal city of Sirte, he said the UN is "very concerned" by an alarming military build-up around that city, including "a high level of direct foreign interference" in violation of a UN arms embargo, Security Council resolutions and commitments made at the Berlin International Conference on Libya six months ago.

Taking a swipe on GNA's national election call, Guterres warned that prospects for Libya-wide polls are "fragile," given military developments and support from external backers.