Libyan military strongman Khalifa Haftar was holding talks in Athens on Friday, just two days ahead of a peace conference in Berlin which he and the head of Tripoli's UN-recognised government Fayez al-Sarraj are expected to attend.
His visit comes as world powers step up efforts for a lasting ceasefire, nine months since an assault on Tripoli by Haftar's forces sparked fighting that has killed more than 280 civilians and 2,000 fighters and displaced tens of thousands.
An interim truce that came into force on Sunday has mostly held, despite accusations of violations from Haftar's forces and the rival Tripoli-based Government of National Accord (GNA).
Haftar walked away from ceasefire talks in Moscow on Monday, but German Foreign Minister Heiko Maas visited his eastern Libya stronghold of Benghazi on Thursday to persuade him to join the Berlin conference.
He flew to Athens on a surprise visit on Thursday, with Greece seeking to build ties with Haftar after the GNA signed a maritime and military cooperation deal with Turkey in November.
Athens is vehemently opposed to the contentious Turkish deal with Libya, which claims much of the Mediterranean for energy exploration, conflicting with rival claims by Greece and Cyprus.
Haftar met Greek Foreign Minister Nikos Dendias after his arrival on Thursday and they were holding further talks on Friday. He is also set to meet Prime Minister Kyriakos Mitsotakis.
Greece is seeking to take part in the Berlin talks but has yet to be invited.
Haftar agreed in principle Thursday to go to Berlin after Sarraj signalled he would be present, Germany's Maas said, adding that he had agreed to abide by the current ceasefire.
He "wants to contribute to the success of the Libyan conference in Berlin and is in principle ready to participate in it," he tweeted, calling it "the best chance in a long time" for peace.
But Sarraj, whose GNA did sign up to a permanent truce deal in Moscow, cast doubt over Haftar's intentions after he refused to also sign.
Haftar "has chosen not to sign the agreement and asked for a delay", he said, calling that "an attempt to undermine the Berlin conference before it starts".
The oil-rich North African state has been in turmoil since a 2011 NATO-backed uprising that overthrew and killed dictator Moamer Kadhafi, and multiple foreign powers have become embroiled.
The GNA is backed by Turkey and Qatar, while Haftar, who backs a rival administration in Libya's east, has the support of neighbouring Egypt as well as Russia and the United Arab Emirates.
The United Nations said the Berlin talks aim to end foreign interference and division over Libya.
US Secretary of State Mike Pompeo will take part and voice support for truce efforts, the State Department said Thursday.
UN Secretary-General Antonio Guterres called Wednesday for firm support for the peace talks and asked for a halt in the fighting.
In a report to the Security Council he urged all parties to "engage constructively towards that end, including within the Berlin process".
Guterres also warned against "external interference", saying it would "deepen the ongoing conflict and further complicate efforts to reach a clear international commitment to a peaceful resolution of the underlying crisis".
The conference will aim to agree six points including a permanent ceasefire, implementation of a much-violated UN arms embargo and a return to political efforts for peace, Guterres said.
Turkish troops have been deployed to support the GNA, while Russia, despite its denials, is suspected of supporting Haftar with weapons, money and mercenaries.
Some 11 countries and several international organisations are set to attend along with the Libyan parties.
The fighting has spurred a growing exodus of migrants, many embarking on rickety boats towards Italy.
Nearly 1,000 intercepted at sea have been forced to return to the war-ravaged country since January 1, mostly ending up in detention, the UN's International Organization for Migration said Tuesday.