KYIV, Ukraine -- With the eyes of the world glued to Israel and Gaza, Russia is waging a major new offensive in eastern Ukraine, mounting the largest push it has attempted since last winter.

Thousands of Russian troops and hundreds of tanks and armored vehicles have been sent into the offensive operations, which began around a week ago and have seen Russia suffer severe casualties while making minor gains, according to Ukrainian officials and independent researchers.

The Russian offensive operations are focused mainly on two areas in eastern Ukraine—the strategic city of Avdiivka and further north near Kupiansk, a city Ukraine liberated in a counteroffensive last year.

Local Ukrainian officials on Monday said the intensity of the Russian assaults on Avdiivka had fallen sharply, likely due to the heavy losses, but that they expected they would resume again and that Russia still had substantial forces.

"The air has come out of them," Vitaliy Barabash, the head of Avdiivka's military administration, told Ukrainian television on Monday. But other Ukrainian officials said they believed the Russian forces were regrouping despite their heavy losses and were still capable of mounting large attacks.

The scale of the new offensive appeared to suggest the Kremlin is seeking to turn the tide of the war after months of defending against Ukraine's counteroffensive. Despite the new Russian attacks, Ukraine is also continuing that offensive, focused in the south.

Russian President Vladimir Putin, in an interview aired Sunday, claimed the new offensives were part of an "active defense" aimed at improving Russian positions in the face of Ukraine's counteroffensive.

The assault on Avdiivka began around a week ago when dozens of tanks and armored vehicles attacked Ukrainian positions from the north and south. Ukrainian officials have said Russia has moved up roughly three brigades, consisting of around 10,000 troops, to support the operation.

Russia is attempting to encircle Avdiivka, which is one of the most heavily fortified areas of the frontline, bordering the Russian occupied regional capital, Donetsk. Russian forces tried to take Avdiivka back in 2014, and the network of deep bunkers and trenches Ukraine has constructed there in the eight years since means since Russia has not been able to advance there since its full-scale invasion last year.

Some Ukrainian officials have said they believe Russia's goal is to try to achieve a victory with Avdiivka and seize more of the Donbas region before next year when Putin will have to manage an election.

But Russia's initial mass assaults involving large numbers of armored vehicles appear to have fared badly, repeating failures from other attacks earlier in the war. Videos released by Ukrainian units near Avdiivka appear to show Russian tanks and armored personnel carriers, sometimes advancing in columns, facing withering Ukrainian fire. Ukrainian military officials said the Russian attacks had run afoul of minefields and been pummeled by artillery, kamikaze drones and anti-tank missiles.

The videos appeared to show dozens of destroyed tanks and armored vehicles, with the bodies of Russian soldiers scattered around them.

Ukraine's general staff and other Ukrainian military officials have claimed Russia has lost over three thousand soldiers since the offensive began, as well as hundreds of vehicles. Although those numbers could not be independently verified, the videos circulating of the attacks suggested Russian casualties had been heavy.

So far Russia has only been able to advance a few hundred meters, according to Ukrainian military officials, with Ukrainian lines largely holding.

Ukrainian soldiers and officials near Avdiivka have said Russian forces have changed tactics since their initial losses, withdrawing their armor further back and now sending in smaller groups of soldiers to probe Ukraine's defenses. Russia is also again using convicts recruited from prisons, in so-called 'Storm Z' detachments.

Andriy Serhan, commander of the drone platoon from the 59th Separate Motorized Infantry Brigade near Avdiivka told Radio Svoboda that there was a lull in the attacks but they were digging in for more attempts.

"We are preparing for the fact that there will be another assault. They are quite strong, powerful," Serhan told Radio Svoboda.

The Russian offensive further norther near Kupiansk was also continuing on Monday, according to Ukrainian officials.

Ilya Yevlash, spokesman for Ukraine's Khortitsa group of forces, said roughly 50,000 Russian troops were concentrated in the region near Kupiansk. There Russian forces were also attacking in smaller groups of 10-20 men, supported by heavy armor and frequent airstrikes, he said.

Ukrainian forces are continuing their own grinding offensive in the southern Zaporizhzhia region and around the key eastern city of Bakhmut, claiming to make minor gains there in recent days.