BERLIN — When top American and European officials gather in Berlin for a one-day summit on Sunday, they will try to persuade Libya's warring sides — and their main international backers — to reach a cease-fire, respect a U.N. arms embargo and pave the way to a political resolution.

The United States and Europe are hoping to regain their credibility and have a greater say in Libya’s future — as their rivals Russia and Turkey extend their influence into North Africa and the Mediterranean Sea.

In a sign of Washington’s growing concern, Secretary of State Mike Pompeo will attend Sunday’s summit, making him the most senior U.S. official to attend a high-level meeting on ending the war in Libya.

Libya has become the center of one of the world’s most internationalized proxy wars, a contest over lucrative oil and gas resources, territory, ideological and geostrategic ambitions. By aiding the rival sides, more than a half-dozen countries are openly breaking the arms embargo, and some are committing possible war crimes.

The United Arab Emirates, Egypt, Saudi Arabia, Jordan, France and Russia are backing eastern commander Khalifa Hifter’s offensive on the Libyan capital, Tripoli. Turkey, Qatar, Italy and other European nations are supporting the U.N.-installed Tripoli government. Since April, several thousand people have been killed or wounded by the conflict, and more than 150,000 people have fled their homes.

Expectations are low for forging a lasting cease-fire at the summit.

For years, European nations saw Libya through the prism of combating terrorism and preventing migrants from crossing the Mediterranean. Washington’s engagement in Libya has been scant since the 2012 attack on a U.S. diplomatic station in Benghazi that killed the U.S. ambassador and three others.

Blatant violations of the arms embargo, the targeting of civilians, the escalation of the war — all were met by relative silence from Europe and Washington.

It’s a different Libya today.

In recent weeks, both Russia and Turkey have stepped into the diplomatic and security vacuum, supporting rival sides, determined to shape the fate of Libya. The United States is worried about Moscow’s growing role, including the presence of Russian mercenaries helping Hifter’s forces with high-tech weaponry, intelligence and sophisticated combat tactics.

The European Union is concerned about Turkey, which is backing the Tripoli government with troops, drones and weaponry. Ankara has signed a controversial oil and gas drilling deal in the eastern Mediterranean Sea that threatens to sideline the economic ambitions of several E.U. nations, including Greece and Cyprus.

“This opens a whole new bag of snakes in terms of the threat profile of Libya for Europe,” said Tarek Megerisi, a Libya analyst at the European Council on Foreign Relations. “Less so for the United States, although this question of Russia having a very prominent position so close to a NATO base in Sicily is probably ringing alarm bells.

“We certainly saw that the U.S. got more engaged in Libya after they saw Russians on the front lines.”

Perhaps the greatest public indication of Europe viewing Turkey and Russia as new threats in their backyard are recent comments by Josep Borrell, the European Union’s foreign policy head. He has warned about the perils of Turkish military involvement in Libya if the Europeans do not actively step up their engagement.

“Nobody will be very happy if, on the Libyan coast, there is a ring of military bases from the Russian and Turkish navies in front of the Italian coast,” Borrell told the European Parliament this past week.

He later wrote in a tweet: “We Europeans barricade ourselves behind the mantra that there can be no military solution to the crisis in Libya. But this is something that could very much happen. We need to engage strongly, keep Libya united and find a peaceful solution to this conflict.”

When German Chancellor Angela Merkel and the United Nations hatched up the Berlin meeting this summer, Hifter’s forces were stuck on Tripoli’s southern edges.

The 76-year-old commander, a dual U.S.-Libyan citizen who lived for years in Northern Virginia, was losing support of some eastern tribes. The Tripoli government was not getting as much support from Turkey. A military stalemate had hardened.

Then in September, Russian mercenaries emerged on the Tripoli’s front lines. With their help, Hifter’s fighters managed to push forward. By late November, frustrated by the absence of condemnation of Hifter and the Russians by Europe and the United States, the Tripoli government turned to Turkey for help. They dangled the eastern Mediterranean drilling rights as an incentive, angering the Europeans, as well as Egypt, which also covets the sea’s resources.

By January, Turkey was sending troops to Libya. Libyan and security sources say there are several hundred, if not more, pro-Turkey Syrian fighters who are fighting for the Tripoli government on the front lines. Turkey has also sent military advisers and an air-defense system to protect Tripoli’s only functioning airport, said analysts.

Meanwhile, Hifter’s forces this month seized the strategic coastal city of Sirte, the birthplace of Libya’s late dictator Moammar Gaddafi. He was toppled and killed by rebels during the 2011 Arab Spring uprisings and NATO intervention.

Turkey and Russia are eyeing billions of dollars in oil, weapons and construction contracts that were left on the table after Gaddafi’s death. Moscow also views its role in North Africa has a key element of its strategy to gain influence in the Middle East.

The United Arab Emirates, Egypt and Saudi Arabia are wary that Libya could be influenced by Islamists, supported by Turkey.

There are already indications that Hifter is wary of honoring a cease-fire. In Moscow last week, he left abruptly without signing a provisional truce pact that the Tripoli government had signed following pressure from Moscow and Turkey.

Hifter’s departure was widely seen as an embarrassment to Russian President Vladimir Putin, who saw the signing as an important way of expressing Moscow’s newfound influence in Libya.

On the ground in Tripoli, there are troubling signs that both sides are using the lull in the fighting to regroup and get stronger. The Turkish military assistance, especially the air defense system, has made the Tripoli government and the militias aligned with it more confident, analysts said. There have also been reported weapons shipments flown into Hifter’s eastern Libya strongholds, and pro-Hifter tribesmen have called for the closure of oil export terminals.

“This in turn, makes Berlin’s outcomes more uncertain,” said Claudia Gazzini, Libya analyst for the International Crisis Group.

“The question is to what extent those present will genuinely commit to what they are signing,” she added, referring to Sunday’s summit. “Or whether, like they’ve done in the past, they will be paying lip service to it, all the while fueling the winds of war in Libya.”

Loveday Morris contributed to this report.