Heraldo de Madrid - Ukraine president says 'outnumbered' in strategic city Severodonetsk

"We're holding out" in the key city but "there are more of them and they are stronger," Zelensky told journalists in Kyiv, adding that Severodonetsk and neighbouring Lysychansk were both "dead cities now".

With fighting raging in and around Severodonetsk, Russia's Foreign Minister Sergei Lavrov blasted European countries for blocking his plane from travelling to Serbia.

Lavrov repeated Moscow's threat of retaliation if the West supplied more long-range weapons to Ukraine as promised, while Zelensky warned that the blockade on the country's grain stocks could get worse.

With Russia bringing the weight of its artillery to bear around Severodonetsk -- the largest city in the Lugansk region not under Russian control -- more help was promised from abroad.

The United Kingdom said it would follow the United States and send long-range missile systems to Ukraine, defying Russian warnings against supplying them to Kyiv.

Thousands of civilians have been killed and millions forced to flee their homes since President Vladimir Putin ordered Russian troops into Ukraine on February 24.

Fighting since April has been concentrated in the east of the country, where Russian forces have made slow but steady advances after being beaten back from other parts of Ukraine, including the capital Kyiv.

- 'It's a horror show' -

Artillery strikes have intensified on Severodonetsk and Lysychansk, where pensioner Oleksandr Lyakhovets said he had just enough time to save his cat before flames engulfed his flat after it was hit by a Russian missile.

"They shoot here endlessly... It's a horror show," the 67-year-old told AFP.

Lysychansk was among the areas visited Sunday by President Volodymyr Zelensky, who "got himself acquainted with the operational situation on the front line of defence", the presidency said.

Lavrov on Monday hit out at European countries that prevented his plane passing through their airspace, forcing him to cancel a visit to ally Belgrade.

"The unthinkable has happened... This was a deprivation of a sovereign state of the right to carry out foreign policy," Lavrov told journalists in Moscow.

Lavrov had been due to hold talks with top officials in Belgrade, one of Moscow's few remaining allies in Europe since the launch of its military offensive in Ukraine.

Serbian daily Vecernje Novosti reported that NATO-members Bulgaria, North Macedonia and Montenegro had refused access to their airspace.

While Serbia has condemned Russia's military action in Ukraine, it has not joined the European Union in imposing sanctions in Moscow, despite its bid to join the bloc.

- UK pledges missiles -

The United States last week said it would supply Ukraine with advanced missile systems, the latest in a long list of weaponry sent or pledged to the pro-Western country.

Lavrov told journalists Monday: "The more long-range weapons you supply, the further we will push away from our territory" the line of Ukrainian forces.

Putin had already warned the West against supplying such weapons.

The UK defence ministry said London had coordinated closely with Washington over its gift of the multiple-launch rocket systems, known as MLRS.

The M270 launchers, which can strike targets up to 80 kilometres (50 miles) away with precision-guided rockets, will "offer a significant boost in capability for the Ukrainian forces", the ministry added.

Western powers have imposed increasingly stringent sanctions on Russia but divisions have emerged on how to act, particularly on whether to engage in dialogue with Russia.

- Resort deaths -

Russian forces continued their offensive on several other fronts in the east of Ukraine, with Kyiv saying it had repulsed seven attacks around Donetsk and Lugansk.

The Russian defence ministry said its aircraft had hit three arms depots and a fuel storage facility near the village of Kodema, in the Donetsk region.

Three civilians were killed in Black Sea resort Lazurne, where Russians have mined the coast, the authorities said.

Renewed Russian long-range missile strikes in the northeastern Kharkiv region hit what Moscow said was a factory for repairing armoured vehicles near Lozova.

At least 10 civilians have been killed in the region in 24 hours, Kyiv said.

"The enemy is stepping up" attacks on infrastructure including roads and "creating railway pontoon bridges across rivers" around Kharkiv, the Ukrainian defence ministry said.

Russian troops now occupy a fifth of Ukraine's territory, according to Kyiv, and Moscow has imposed a blockade on its Black Sea ports, sparking fears of a global food crisis.

Zelensky warned Monday the volume of grain his country is unable to export because of a Russian blockade could at least triple by the autumn.

"Right now we have about 20-25 million tonnes blocked. In the autumn that could be 70-75 million tonnes," said Zelensky, whose country was the world's fourth biggest grain exporter before the war.

The Ukrainian army said meanwhile that it had pushed the Russian fleet back more than a hundred kilometres from Ukraine's southwestern Black Sea coast, where Moscow's ships have been carrying out a naval blockade for weeks.

According to the ministry, Russian forces had to deploy coastal defence missile systems in Crimea and in Ukraine's southern Kherson region which they now occupy.

"We have deprived the Russian fleet of total control over the northwestern part of the Black Sea, which has become a 'grey zone'," the ministry said, adding Moscow was currently trying to regain control there.

Russian ships nevertheless continue "to block civil navigation" in this area, according to the same source.

W.Hidalgo--HdM