Marathon talks on ending the war in Ukraine lasted through the night into the 14th hour on Thursday as the leaders of Russia, Ukraine, France and Germany sought to untangle a complicated skein of military and political issues.

More than 5,300 people have died since April in the fighting between Ukrainian forces and Russia-backed separatists in two eastern provinces and the bloodshed rose sharply in recent weeks.

Despite the ongoing talks, both rebels and government troops reported fighting across eastern Ukraine.

As President Barack Obama considers rising calls at home for sending U.S. lethal aid to Ukraine, European leaders fear that would only aggravate the fight. Russia, meanwhile, faces a severe economic downturn driven in part by sanctions the West has imposed for supporting the separatists with troops and equipment, which Russia vehemently denies it is doing.

The urgency felt by all sides appeared to be underlined by the extraordinary length and discomfort of the talks between the leaders of Ukraine, Russia, France and Germany. They sat down with each other Wednesday evening in the Belarusian capital and the talks continued through the night for more than 14 hours as crowds of reporters waited anxiously for outcome of the talks in a marble-floored, chandeliered convention hall in Minsk.

Officials have remained tight-lipped, praising progress but refusing to divulge details.

In a diplomatic blitz that began last week, German Chancellor Angela Merkel and French President Francois Hollande visited Kiev and Moscow to speak to Ukrainian President Petro Poroshenko and Russian President Vladimir Putin, paving the way for the marathon session in Minsk.

"The entire world is waiting to see whether the situation moves toward de-escalation, weapons pullback, cease-fire, or ... spins out of control," Poroshenko said upon arriving.

Russian Foreign Minister Sergey Lavrov signaled some progress, saying late Wednesday that the talks were "active, better than super." But it was unclear when a decision might be announced — and how soon the shooting would stop if an agreement is reached.

A top rebel official, Andrei Purgin, told Russian television that it might take a day or more for hostilities to end even if a cease-fire is called.

Details of a possible peace deal haven't been released, but key sticking points include:

— Drawing a new line of division: Ukraine wants the same one that was agreed upon in September, while Russia wants a new line that reflects the rebels' significant territorial gains since then.

— Withdrawing Russian troops and equipment from eastern Ukraine: Russia says it does not have any troops and military hardware in the east, a stance scoffed at by Ukraine and NATO.

— Securing the Ukraine-Russia border: Ukraine wants to regain control of its border with Russia to stem the flow of Russian fighters and weapons, while Russia says that's up to the rebels who have captured some key border posts.

— Giving the separatists more autonomy: Ukraine says it may offer them broad rights under Ukrainian law but Russia wants guarantees. Russia also wants Ukraine to end its financial blockade of the east.

At a news conference in Moscow, Lavrov said there was "notable progress" in the peace process, but gave no details. He said the most important goal of the talks would be to implement a cease-fire, but warned that Ukraine only could fully re-establish its control over the border with Russia if it offers a degree of autonomy to the east and lifts its economic blockade.

"To give away the Russian part of the border also would be to cut them (the rebels) off even from humanitarian help and allow them to be surrounded," Lavrov said.

Earlier on Wednesday, French Foreign Minister Laurent Fabius said that "quite a number of problems remain" in negotiations, including the future of eastern Ukraine, guarantees about the Ukraine-Russia border, and the prospects of a possible cease-fire, weapons pullback and prisoner exchange.

Fabius said the aim of the talks is to win an accord that works on the ground, "not just one on paper."

Germany and France rushed to mediate after a recent surge in fighting that continued Wednesday.

In the rebel-held city of Donetsk, rebel officials said five people were killed and nine wounded in a shelling attack on a bus station. Officials in Kiev said 19 troops were also killed in fighting in Debaltseve, a hotly contested transport hub in eastern Ukraine.

Poroshenko posted a statement saying he had made an impromptu visit early Wednesday to the eastern Ukrainian city of Kramatorsk, where Kiev says 16 people were killed and 48 wounded in a rocket strike a day earlier. The city is 30 miles (50 kilometers) from the nearest front line.

"We demand an unconditional peace," Poroshenko said. "We demand a cease-fire, a withdrawal of all foreign troops, and closing of the border. ... We will find a compromise within the country."

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Associated Press writers Peter Leonard in Donetsk, Ukraine, and Laura Mills, Vladimir Isachenkov and Jim Heintz in Moscow contributed to this report.