Libya's warring sides have begun to engage in a new round of ceasefire talks, the United Nations said on Wednesday, after rapid gains by the UN-backed government ended with heavy fighting around the central coastal city of Sirte. 

The Government of National Accord (GNA), which is backed by Turkey, and the eastern-based Libyan National Army (LNA), backed by the United Arab Emirates, Russia and Egypt, have each met separately with UN negotiators, the UN Libya mission said. 

It follows the sudden collapse of the LNA's 14-month offensive to capture the capital Tripoli, the seat of the GNA, and its retreat from most of its territory in northwest Libya. 

A GNA effort from Monday to push further east and capture Sirte, effectively wiping out all the LNA's gains since the start of its Tripoli campaign in April 2019, was repulsed with air strikes, an LNA military source said. 

"The Mission is particularly concerned by reports of escalation and mobilization in and around the city of Sirte," the UN Libya mission said in its statement announcing the talks were under way. 

It said it had verified at least 19 civilian deaths in Sirte. 

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Libya has been locked in a civil war since the ouster and killing of former leader Muammar Gaddafi in 2011. The situation escalated in 2014, splitting power between two rival governments: the UN-backed GNA based in the capital Tripoli and a government in the northeastern city of Tobruk allied with the Khalifa Haftar-led LNA.

 In a State Department press briefing Wednesday, U.S. Secretary of State Mike Pompeo called the agreement between the GNA and LNA to re-enter UN security talks a very positive step. 
  
"Quick and good faith negotiations are now required to implement a ceasefire and relaunch the UN-led intra-Libyan political talks," he said, urging "all Libyans on all sides to act" to avoid foreign intervention. 
  
Later in the day, the White House said in a statement that President Donald Trump had held a phone conversation on Libya with his Egyptian counterpart Abdel-Fattah al-Sisi, in which Trump praised Sisi's efforts to promote political reconciliation and de-escalation in the Libyan conflict. 
  
"The two leaders discussed ways to resume the United Nations' 5+5 ceasefire talks and the departure of all foreign forces from Libya," the statement added. 

The Egyptian president announced on June 6 an initiative to end the Libyan conflict following his meeting in Cairo with commander Haftar.

Russian President Vladimir Putin and his Turkish counterpart Recep Tayyip Erdogan also discussed the situation in Libya in a phone conversation on Wednesday, the Kremlin said in a statement. 
  
The two leaders expressed deep concern about the ongoing large-scale clashes in the North African country, which led to numerous casualties and destruction, the statement said. 
  
Putin noted the importance of an early ceasefire and the resumption of intra-Libyan dialogue based on the decisions of the Berlin International Conference on January 19, 2020, and approved by UN Security Council Resolution 2510, as well as other initiatives aimed at a political and diplomatic settlement of the conflict, it said. 

(With input from Reuters, Xinhua)