Ukrainian President Volodymyr Zelensky has said Russia was deliberately cutting supplies of natural gas to impose a "price terror" against Europe, and he called for more sanctions on Russia.
"Using Gazprom, Moscow is doing all it can to make this coming winter as harsh as possible for the European countries. Terror must be answered - impose sanctions," he said in a late-night video address.
His comments come after European Union countries approved a weakened emergency proposal to curb their gas demand as they try to wean themselves off Russian energy and prepare for a possible total cut-off.
Russia has said it will cut gas supplies to Europe from tomorrow, while missile attacks in Black Sea coastal regions raised doubts about whether Russia will stick to a deal to let Ukraine export grain.
The Kremlin said the gas disruption is the result of maintenance issues and Western sanctions, while the European Union has accused Russia of energy blackmail.
Politicians in Europe have repeatedly said Russia could cutoff gas this winter, a step that would thrust Germany into recession and hurt consumers already hit by soaring inflation.
Russia has said it was not interested in a complete stoppage of gas supplies to Europe.
Adding to concerns on the energy front, the Ukrainian state pipeline operator company said Russian gas giant Gazprom without prior notice has increased pressure sharply in a pipeline that runs through Ukraine to deliver Russian gas to Europe.
Such pressure spikes could lead to emergencies including pipeline ruptures, and pipeline operators are obliged to inform each other about them in advance, the Ukrainian company said.
The first ships from Ukraine may set sail in days under a deal agreed on Friday, the United Nations said, despite a Russian missile attack on the Ukrainian port of Odesa over the weekend
A spokesman for the military administration said another missile had hit the Odesa region this morning.
Meanwhile, the Ukrainian military has reported Russian cruise missile strikes in the south and that Ukrainian forces had hit enemy targets.
Serhiy Bratchuk, a spokesman from the military administration in Odesa, told a Ukrainian television channel that a missile fired from the direction of the Black Sea had struck the region, but gave no information on casualties.
East of Odesa along the Black Sea coast, port infrastructure at Mykolaiv was damaged by an attack, according to the mayor Oleksandr Senkevich.
Russia's defence ministry did not immediately reply to an out-of-hours request for comment.
Read more: Latest Ukraine stories
A major fire broke out at an oil depot in the Budyonnovsky district of Russian-backed Donetsk People's Republic in eastern Ukraine after Ukrainian troops shelled the province, Russia's TASS reported, quoting a reporter at the scene.
No casualties or injuries have been reported.
Before the invasion and subsequent sanctions, Russia and Ukraine accounted for nearly a third of global wheat exports.
Officials from Russia, Turkey, Ukraine and the United Nations agreed on Friday there would be no attacks on merchant ships moving through the Black Sea to Turkey's Bosphorus Strait and on to markets.
Moscow brushed aside concerns the deal could be derailed by a Russian attack on Odesa on Saturday, saying it targeted only military infrastructure.
The White House said the strike cast doubt on Russia's credibility and was watching closely to see if commitments would be fulfilled.
"We will also continue to actively explore other options with the international community to increase Ukraine exports through overland routes," it said.
Russia's Black Sea fleet has blocked grain exports from Ukraine since Moscow's February invasion.
Moscow blames Western sanctions for slowing its food and fertiliser exports and Ukraine for mining the approaches to its ports.
Under Friday's deal, pilots will guide ships along safe channels through the naval minefields.
A Ukrainian government official said he hoped the first grain shipment could be made from Chornomorsk this week, with shipments from other ports within two weeks.
Mr Zelensky was adamant that trade would resume.
"We will start exporting, and let the partners take care of security," he said.
Russian Foreign Minister Sergei Lavrov, on a tour of African countries, said there were no barriers to the export of grain and nothing in the deal prevented Russia from attacking military infrastructure.
The Kremlin also said the United Nations must ensure curbs on Russian fertiliser and other exports were lifted for the grain deal to work.
The Kremlin says it is engaged in a "special military operation" to demilitarise Ukraine. Both the Ukrainian government and Western allies say the war is an unprovoked act of aggression.
Thousands of civilians have died and millions have fled during the war. Russian artillery barrages and air strikes have pulverised cities.
With Western weapons boosting the Ukrainians, Vladimir Putin's forces are making slow progress but they are believed to be readying for a new push in the east.
Ukraine said its forces had used US-supplied HIMARS rocket systems to destroy 50 Russian ammunition depots since receiving the weapons last month.
Russia did not comment but its defence ministry said its forces had destroyed an ammunition depot for HIMARS systems.