Ukraine's Armed Forces Commander-in-Chief Valeriy Zaluzhny said Sunday that he told his American counterpart, Gen. Mark Milley, U.S. Chairman of the Joint Chiefs of Staff, that Russian firepower superiority in the Luhansk region is far greater than that of Ukrainian forces.

Zaluzhny said that during a briefing he told Milley that Russian forces are concentrating their efforts in the north of the Luhansk region, where they are using artillery "en masse" and their firepower superiority is 10 times that of Ukraine's.

"Despite everything, we keep holding our positions," Zaluzhny said.

Zaluzhny also said Russia has deployed up to seven battalion tactical groups in Severdonetsk, a city in the Luhansk region. He said Russian shelling of residential areas in Kharkiv in northeast Ukraine has resumed.

Russian forces destroyed a second bridge leading into Severodonetsk and are now targeting a third bridge in an effort to completely cut off the city, Luhansk region Gov. Sergiy Haidai said Sunday. Ukraine's army still controls around one third of the city, he said.

Haidai said that Ukrainian forces are still holding onto the Azot chemical plant in Severodonetsk, where around 500 civilians are taking shelter.

If Severodonetsk falls, Lysychansk will be the only city in the Luhansk region that remains under Ukraine's control.

Zaluzhny said that as of Sunday, the front line of the war stretched 1,522 miles and that active combat was taking place on at least 686 miles of the front line.

Zaluzhny said that during his briefing with Milley, he reiterated Ukraine's urgent request for more 155 mm caliber artillery systems.

Russia claims a cruise missile strike destroyed a large warehouse in western Ukraine storing weapons supplied to the Ukrainians by the United States and European allies.

While police in the Ternopil region of Ukraine, where at least one cruise missile hit, told ABC News that no weapons were destroyed, the region’s governor said part of a military facility was damaged.

Ternopil's governor Volodymyr Trush posted a video showing widespread damage from what he said were four Russian missiles launched Saturday from the Black Sea. Trush said 22 people were wounded, including a 12-year-old child, in the missile strikes.

In addition to the military facility, Trush said four five-story residential apartment buildings were damaged. One of the missiles hit a gas pipeline, he said.

Russia’s defense ministry said Kalibr high presicion sea-based, long-range missiles struck near Chortkiv in the Ternopil province and destroyed a large warehouse full of anti-tank missile systems, portable anti-aircraft missile systems and artillery shells supplied by the United States and European countries.

A new era for Russia's fast-food and economic scene dawned on Sunday as McDonald's restaurants flung open their doors in Moscow under new Russian ownership and with the new name "Vkusno & tochka," which translates as "Tasty and that's it.”

Alexander Govor, the new owner of the chain, attended a ribbon cutting ceremony at what was once McDonald's flagship restaurant in central Moscow, before the first customers were granted entry, met with cheering and applause from restaurant staff.

Scores of people lined outside the flagship Moscow restaurant, which is among 15 rebranded outlets that will initially open in and around the capital on Sunday.

The queue was significantly smaller than the thousands of people who thronged to the original McDonald's opening there in 1990 during the Soviet era.

Oleg Paroev, chief executive of Vkusno & tochka, said the company was planning to reopen 200 restaurants in Russia by the end of June and all 850 by the end of the summer.

The chain will keep its old McDonald's interior but will expunge any references to its former name, said Paroev, who was appointed Russia McDonald's CEO weeks before Moscow sent tens of thousands of troops into Ukraine on Feb. 24.

McDonald's closed its restaurants in Russia on March 14 and said in mid-May it decided to leave the market.

-ABC News’ Rashid Haddou

European Commission President Ursula von der Leyen met with Ukrainian President Volodymyr Zelenskyy in Kyiv Saturday to discuss his country's bid to get candidacy status to join the European Union.

"The discussions today will enable us to finalize our assessment by the end of next week," von der Leyen said in a joint press conference with Zelenskyy posted on Twitter.

"I must say I highly appreciate the enormous efforts and the determination of Ukraine in this process. The people of Ukraine have proven incredible strength and motivation and stamina. So, I am deeply convinced that we will together, you will overcome this atrocious war. We will, and you will, rebuild this beautiful country and modernize Ukraine," von der Leyen said.

Von der Leyen said this is her second visit to Kyiv.

"The brutal fighting continues in the east and in the south. But I must say it is impressive to see how strong the Ukrainians are defending, courageously, their country in this very difficult conditions," Von der Leyen said.

-ABC News' Somayeh Malekian

President Joe Biden on Thursday announced a new $800 million security assistance package to help Ukrainians fighting in the eastern Donbas region. This funding includes heavy artillery weapons, tactical drones and howitzers.

This package includes 72 new howitzers. Combined with the 18 howitzers announced last week, the 90 howitzers headed to Ukraine can equip five battalions, according to the administration.

Biden noted that he’s run out of pre-approved money and equipment to send to Ukraine and he appealed to Congress to approve more.

When pressed by ABC News on how long the U.S. can sustain this level of spending, Biden said, “We have the capacity to do this for a long time."

He went on, "The question is, are we going to continue to maintain the support of the international community? And keep the pressure on Putin to prevent him from overrunning the country, No. 1, and No. 2, make sure we continue to maintain the economic sanctions, which, over time, and we're beginning to see, they’re devastating their economy and their ability to move forward."

Biden also announced a separate $500 million in economic aid to Ukraine to help fund government operations like salaries, pensions and social programs.

The president added that the U.S. is now banning Russian-affiliated ships from American ports.

Biden met with Ukrainian Prime Minister Denys Shmyhal Thursday morning ahead of his remarks.

-ABC News' Luis Martinez and Sarah Kolinovsky