The announcement by Gazprom was sudden.

Russia's state-owned gas company on Monday announced an unexpected, drastic cut in supply to Europe, leading Ukraine to call the West to action over the "gas war".

The gas cuts came amid guarded hope of resuming exports this week of another key commodity — Ukraine's grain — under a breakthrough deal that was called into question by a strike by Moscow on the key port of Odessa.

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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, and a spokesman for the military administration in the saying another missile had hit the Odesa region on Tuesday morning.

Soaring energy costs and the threat of hunger faced by millions in poorer nations show how the biggest conflict in Europe since World War Two, now in its sixth month, is having an impact far beyond Ukraine.

The company (Gazprom) said it was halting the operation due to the "technical condition of the engine".

Gazprom, the Russian energy giant, said it was cutting daily deliveries of gas to Europe via the Nord Stream pipeline to 33 million cubic metres a day — about 20 per cent of the pipeline's capacity — from Wednesday.

That is half of the current flows, which are already only 40% of normal capacity. Prior to the war, Europe imported about 40% of its gas and 30% of its oil from Russia.

The company (Gazprom) said it was halting the operation of one of the last two operating turbines due to the "technical condition of the engine".

But Germany -- which is heavily reliant on Russian gas but has looked to wean itself off gradually following Moscow's February 24 invasion of Ukraine -- said there was no technical justification for the cut.

German group Siemens Energy, which is charged with maintaining the turbine, also said in a statement to AFP that it saw "no link between the turbine and the gas cuts that have been implemented or announced".

European Union countries are set to approve on Tuesday 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.

Soaring energy costs and the threat of hunger faced by millions in poorer nations show how the biggest conflict.

The Ukrainian military on Tuesday 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.

Ukrainian President Volodymyr Zelensky said that the cuts showed that Europe should bolster sanctions against Russia.

"This is an open gas war that Russia is waging against a united Europe," Zelensky said.

"They don't care what will happen to the people, how they will suffer -- from hunger due to blocked ports, from winter cold and poverty... or the occupation. These are just different forms of terror," he said in his daily video message.

"That is why you have to hit back. Do not think about how to bring back the turbine, but strengthen the sanctions," he said.

The Russian announcement came on the same day that Ukraine announced receiving the first of an expected 15 Gepard anti-aircraft systems and tens of thousands of shells from Germany.