KYIV (REUTERS, NYTIMES) -  Ukraine’s President Volodymyr Zelensky predicted Russia will escalate its attacks this week as European Union (EU) leaders consider whether to back Kyiv’s bid to join the bloc and Moscow presses its campaign to win control of the country’s east.

“Obviously, this week we should expect from Russia an intensification of its hostile activities,” Mr Zelensky said in his Sunday (June 19) nightly video address.

“We are preparing. We are ready.”

Ukraine applied to join the EU four days after Russian troops poured across its border in February.

The EU’s executive, the European Commission, on Friday recommended that Ukraine receive candidate status.

Leaders of the 27-nation union will consider the question at a summit on Thursday and Friday and are expected to endorse Ukraine’s application despite misgivings from some member states. The process could take many years to complete.

The EU’s embrace of Ukraine would interfere with one of Russian President Vladimir Putin’s stated goals when he ordered his troops into Ukraine: To keep Moscow’s southern neighbour outside of the West’s sphere of influence.

Mr Putin on Friday said Moscow had “nothing against” Ukraine’s EU membership, but a Kremlin spokesman said Russia was closely following Kyiv’s bid especially in light of increased defence cooperation among member countries.

Meanwhile, Russian forces appeared poised to tighten the noose around thousands of Ukrainian troops near two strategically important cities in the fiercely contested Donbas region of eastern Ukraine on Sunday, mounting an assault on Ukrainian front lines that forced Ukraine to rush reinforcements to the area.

On a day of fighting that put even territory thought to be securely in Ukrainian hands in play, Prime Minister Boris Johnson of Britain and the North Atlantic Treaty Organisation (Nato)secretary-general, Jens Stoltenberg, warned that the war could grind on for years.

They urged Ukraine's Western allies to settle in for the long haul as Russia moved aggressively to wear Ukraine down through what Mr Johnson, writing in The Sunday Times of London, called a "campaign of attrition".

The Russians made an initial breakthrough Sunday in Toshkivka, a small town southeast of the metropolitan area of Sievierodonetsk and Lysychansk, where vicious street-by-street fighting and artillery duels have raged for weeks.

Mr Sergei Haidai, the regional military governor, acknowledged that the Russians had "had success" in the Toshkivka area but said the occupiers "suffered defeat" after Ukrainian artillery went to Toshkivka's defense.

It was not clear who controlled Toshkivka by nightfall Sunday. If Moscow's forces succeed in eventually surrounding Sievierodonetsk and Lysychansk, however, thousands of Ukrainian fighters defending the two cities could be stranded.

That would deliver a hard-won military victory to the Kremlin and bring Russian forces a step closer to fulfilling President Vladimir Putin's objective of seizing all of Ukraine's eastern Donbas region.

"The heavy fights in Sievierodonetsk are continuing," Mr Haidai said, adding that the Russians had failed and suffered massive losses.

Phone communication in the area is limited, and the bridges leading into Sievierodonetsk have been destroyed, making it difficult to get an accurate picture of the situation there.

The Institute for the Study of War, a Washington research group, said that Russia had made "marginal gains" around the city but that its offensive across the rest of Donbas had "largely stalled."

"Russian forces will likely be able to seize Sievierodonetsk in the coming weeks, but at the cost of concentrating most of their available forces in this small area," the institute said in its latest assessment.

Russia's Defence Ministry said Russian soldiers and Moscow-backed separatists had also claimed control of Metolkine, just southeast of Sievierodonetsk.

Russian state news agency Tass said that many Ukrainian fighters had surrendered there, although it was not possible to verify the assertions independently.

As the Sievierodonetsk area fell deeper into peril Sunday, intensifying Russian attacks across much of Ukraine - including renewed shelling near Kharkiv in the north, strikes at Mykolaiv in the south and destruction of infrastructure in the country's east and central regions - made clear that the war could still flare up far beyond Donbas, where Russia has refocused its military efforts after failing to capture Kyiv in the spring.

Ukraine faces an increasingly grim and bloody fight in its east, where Russia is using long-range artillery to bombard cities and military positions. Ukrainian officials have complained that advanced weaponry from their allies is arriving too slowly to overturn Russia's firepower advantages and that as many as 200 Ukrainian soldiers are being killed daily.

In the northeastern city of Kharkiv, Ukraine's second largest, where Russian forces were pushed out several weeks ago, Russian missiles hit a tank repair plant, a Russian military spokesman said Sunday, destroying what the Russian Defence Ministry said were two Urugan rocket launchers.

Mr Vadym Denysenko, an adviser to Ukraine's interior minister, said Sunday that "Russia is trying to make Kharkiv a front-line city," describing the situation there as difficult.

Russian strikes also targeted a gas processing plant near the eastern city of Izium, causing a large fire, and destroyed an oil depot in the central Dneprotrovsk region, killing one person and wounding 11 others, Ukrainian officials said.

In the port city of Mykolaiv, which remains in Ukrainian hands, Ukrainian officials said Russian missiles over the weekend had also destroyed businesses and infrastructure.

Two people were killed in the village of Halystsynove in the same region in a separate strike Saturday, an attack that caused a fire, regional officials said.

But it is in the Donbas, an area of rolling plains, farm fields and coal mining towns not far from the Russian border, that Moscow has committed the bulk of its military power in recent weeks.

The Sievierodonetsk pocket, as military officials call the area around Sievierodonetsk and Lysychansk, is about three-quarters encircled by Russian forces, leaving only a slender gap to the west where Ukrainian troops come and go by village roads that are often shelled by Russia.

If Russian forces succeed in breaking through the defensive lines, they will reduce Ukrainian troops' ability to manoeuvre in the Sievierodonetsk pocket. The advance would also further allow Russian forces to threaten the few remaining supply routes into Lysychansk and Sievierodonetsk, where about 70,000 civilians remain, many of them too elderly or frail to evacuate.

Mr Zelensky said this month that the "fate" of much of eastern Ukraine was being decided in the battle for the two cities.

Their strategic importance partly explains why Ukraine has chosen to hold out in street fighting there, a strategy fraught with risks. Fighting at close range in Sievierodonetsk, the Ukrainian thinking goes, denies Russia the chance to bring its vast advantage in artillery weapons to bear.

But as Russian forces have encircled soldiers in Sievierodonetsk and supporting troops in Lysychansk, Russian artillery gun lines have pummelled roads, bridges and Ukrainian troop positions with thousands of shells fired every day, by Ukrainian estimates.

Still, the street fighting in the city and battles in the fields around it have cost the Russians dearly in lives and equipment, more than the Ukrainians have lost, Ukrainian commanders have said. After months of fighting, the Russian army in Ukraine is exhausted and nearing the limits of its resources, Mr Andriy Zagorodnyuk, a former defence minister of Ukraine, said Sunday in an interview.