Ukraine and Russia's foreign ministers meet their German and French counterparts on Monday in a renewed bid to resolve the smouldering civil war in eastern Ukraine as Moscow seeks to end Western sanctions.
The Ukraine conflict, half-forgotten by the West amid other crises and its own divisions, has claimed over 10,000 lives and still sees daily clashes between pro-Russian and Ukrainian forces.
President Vladimir Putin last Thursday warned that any military "provocations" while Russia hosts the football World Cup would have "very severe consequences for Ukraine as a state".
The UN Security Council condemned "continuous violations of the ceasefire" and "the tragic humanitarian situation" on the frontline, and called for an immediate withdrawal of heavy weapons.
The UN resolution last week was written by France with support from Germany -- the core EU powers that brokered the poorly observed 2015 Minsk peace agreement -- and was adopted unanimously, including by Russia.
After over a year on the back burner as the French, Germans and Russians headed to the polls in 2017 and 2018, Paris, Berlin and Moscow have now turned their focus back on Ukraine ahead of its own elections next year.
German Foreign Minister Heiko Maas, who is hosting the meeting, predicted "tough" talks.
"The implementation of the Minsk accords stalled for too long -- at the expense of the people in eastern Ukraine, who wish for nothing more ardently than peace," he told the daily Bild.
"I have no illusions -- the new start will be difficult. The interests and standpoints of Ukraine and Russia are far apart in many areas."
His French counterpart Jean-Yves Le Drian warned Friday that "the credibility of the current peace process is at stake", given a daily death toll and deteriorating humanitarian situation.
The Berlin meeting is an attempt to restore dialogue between the two sides, which blame each other for the ongoing conflict, and to discuss the more distant goal of a blue-helmet UN peacekeeping force.
Preparing the ground in a rare phone call Saturday, Putin and Ukrainian President Petro Poroshenko discussed an "exchange of people being held" by both sides.
But hopes for a diplomatic breakthrough are low at the Berlin meeting -- the first by the quartet in 16 months -- given the high tensions and deepening distrust between the West and Russia.
After a popular Ukrainian uprising ousted a Kremlin-backed president in Kiev in 2014, Russia moved to annex the Crimea peninsula and back insurgents in the former Soviet state.
Brussels responded to the territorial grab with a series of asset freezes and travel bans as well as stinging economic sanctions, to which Moscow retaliated in kind.
Since then, the US and European powers have accused Moscow of using hackers and propaganda to sow discord, meddle in elections and back eurosceptics and right-wing populists, as well as ramping up military posturing to threaten eastern European states.
In Syria's brutal civil war, which has killed more than 350,000 people and displaced millions, Russia has since 2015 defied the West by unleashing a bombing campaign to support Bashar al-Assad.
Relations hit a new low in March this year, as many western states expelled Russian embassy staff over the alleged poisoning by Moscow of former double agent Sergei Skripal and his daughter Yulia in Britain.
Putin, who was re-elected to a fourth term in March, has denied all the charges and argued forcefully that hostile NATO powers are seeking to demonise and weaken Russia.
Moscow also accused Kiev of spreading "bizarre" fake news after Ukraine's secret service last month staged the murder of Russian journalist Arkady Babchenko, claiming it did so to foil a Russian plot on his life.
Amid the ill will, Ukraine has urged citizens not to travel to Russia for the World Cup, warning they could be arrested on trumped-up spying charges.
Russia's main goal is the lifting of damaging economic sanctions, a push aided by the rise of sympathetic populist parties in the EU, most recently in Italy.
On a visit last week to conservative Austrian Chancellor Sebastian Kurz, whose far-right junior coalition partners back Russia's claim of sovereignty over Crimea, Putin insisted he hoped for a "united and prosperous" European Union and denied any wish to "divide" the bloc.
France and Germany are firm that any sanctions relief for Russia must be conditional on advances in the Ukraine peace process.