Ukrainian President Petro Poroshenko (left) holds a flag during an Independence Day military parade in Kiev on August 24, 2015
Brussels (AFP) - Ties between the EU and Russia remain at their lowest ebb over the conflict in Ukraine, ahead of a series of key talks including a visit by President Petro Poroshenko to Brussels on Thursday.
Renewed fighting in eastern Ukraine between pro-Moscow rebels and Kiev's government forces has made a mockery of a February ceasefire, while the European Union has renewed tough sanctions against Russia.
Poroshenko is set to call for renewed support from the European Union when he travels to Brussels, days after meeting German Chancellor Angela Merkel and French President Francois Hollande in Berlin.
Poroshenko will meet European Commission chief Jean-Claude Juncker and European Council President Donald Tusk for talks centering on the "implementation of the Minsk agreement" that led to the ceasefire, the Commission said last week.
At the same time, the EU is due to restart stalled three-way talks with Kiev and Moscow on Russian gas supplies to Ukraine, and on a landmark EU-Ukraine free-trade deal accord that Moscow says will harm its economy.
"These are the only two dossiers that the Russians agree to discuss with the EU," said Pierre Vimont, former secretary-general of the EU diplomatic service and now researcher for the Carnegie Institute.
"These talks are never easy. The Russians are difficult, and for their part the Ukrainians stick to their ground too."
The EU's condemnation on Tuesday of a jail sentence handed down by a Russian court to Ukrainian filmmaker Oleg Sentsov for "terrorism" added to the bad blood ahead of the meetings.
- Gas war? -
The EU wants at all costs to avoid a "gas war" with Russia as winter looms, with any stand-off threatening supplies to Europe, around half of which pass through Ukraine.
Experts say a deal is needed by October to avoid shortages.
Maros Sefcovic, the EU's Vice President in charge of Energy Union, will on the sidelines of a western Balkans summit in Vienna on Thursday relaunch talks with the Ukrainian side, which has not been supplied by Russian giant Gazprom for several months.
A meeting with Russian Energy Minister Alexander Novak is also scheduled for the start of September.
The trade talks are less urgent but cover highly sensitive ground, as the trade deal was originally the key part of the EU-Ukraine Association Agreement that then-president Viktor Yanukovych backed out of signing in November 2013.
That led to the pro-EU Maidan movement which toppled him, and which was followed by Russia's annexation of Crimea in March 2014 and the fighting in eastern Ukraine which has claimed 6,800 lives.
EU Trade Commissioner Cecilia Malmstroem is due to bring the relevant parties in the trade talks together in Brussels on September 7.
"But trade negotiations are difficult, the Russians have taken a stand on principle, and we have never been able to go into the details and negotiate on concrete matters," Vimont said.
Some Kiev politicians accuse Moscow of planning a new rebel offensive that could rattle the Ukrainian leadership enough to reverse its plans to implement the landmark trade treaty with the European Union at the start of next year.
Russia has already threatened to expand its list of banned Ukrainian food imports should the agreement go into effect.
Yet Poroshenko has said that he and European Commission President Jean-Claude Juncker have agreed by telephone that the "free trade zone should be strengthened as of January 1."
The sanctions that the EU imposed after Crimea were renewed in July, and still poison relations with Moscow.
Putin -- who persistently denies any Kremlin involvement in the crisis and calls Russian soldiers discovered in the war zone "volunteers" -- was notably omitted from the round of meetings between Poroshenko, Hollande and Merkel, despite having been instrumental in arranging the Minsk ceasefire.