Russia-Ukraine updates: Russian missiles hit close to nuclear reactors: IAEA director

Ukrainian forces have "stabilized" the situation along the front line in the eastern and southeastern regions of the country, in large part thanks to U.S.-supplied HIMARS rocket launchers, the Ukrainian military said on Monday.

“We managed to stabilize the situation. It is complex, intense, but completely controlled,” Valery Zaluzhny, the commander-in-chief of the Ukrainian Armed Forces, said.

An important factor contributing to Ukraine's retention of its defensive lines and positions is the timely arrival of U.S. supplied M142 HIMARS -- High Mobility Artillery Rocket System -- rocket launchers, Zaluzhny added. These highly precise and modern weapons have been delivering “targeted strikes” on Russian “control points, ammunition and fuel storage depots,” the top commander added.

Ukrainian troops struck a Russian military facility in the area of ​​an asphalt plant in the eastern town of Nova Kakhovka on Monday, Ukrainian military officials said. Ukrainian forces also hit an administrative building and a hangar filled with Russian fuel tankers in the southern town of Beryslav, killing more than 100 Russian soldiers, the Ukrainian military said on Monday.

Russian forces shelled the town of Nikopol in the Dnipropetrovsk region about 40 times on Monday night, local authorities said. Explosions were also reported in the Odesa region, injuring several civilians. Russian troops also fired cluster shells at the city of Mykolaiv late on Monday.

Russia's stated immediate objective is to seize all of the Donetsk region, the U.K. Ministry of Defense said on Tuesday. Even if Russian troops make further territorial gains, the tempo of their advance is likely to be very slow, the ministry added.

Russian units, severely under-manned, face a dilemma between deploying more forces to the Donbas or defending against Ukrainian counter-attacks in the Kherson area, the observers said.

-ABC News' Edward Szekeres, Yulia Drozd, Max Uzol and Yuriy Zaliznyak

Ukrainian first lady Olena Zelenska will meet with first lady Jill Biden in Washington, D.C., on Tuesday, Biden's office said, one day before Zelenska addresses Congress.

Ukrainian first lady Olena Zelenska will make remarks Wednesday before members of Congress on Capitol Hill, House Speaker Nancy Pelosi announced.

All members of the House and Senate are invited to the event, which is set for 11 a.m ET.

Russian Defense Minister Sergei Shoigu has visited the East group of Russian forces involved in the fighting in Ukraine and ordered his troops to eliminate the Ukrainian army's long-range missiles and artillery ammunition it uses to shell targets in the Donbas region, the Russian Defense Ministry said on Monday.

Shoigu instructed the group's commander to give priority to the use of precision-guided weapons to destroy Ukraine's long-range missile and artillery assets, the ministry added. Russia has accused Ukraine of using its long-range weapons to shell residential neighborhoods in Donbas communities and set fire to wheat fields and grain storage facilities.

Ukrainian officials said Russian missiles struck targets across much of eastern Ukraine on Sunday and early Monday.

Six people were killed in the town of Toretsk in the Donetsk region after Russian shelling, the state emergency service said. Missiles also struck civilian infrastructure, including a school in the Dnipropetrovsk and Odesa regions.

Russia also carried out 55 strikes on the Sumy region on Sunday. Around 60 projectiles landed in Nikopol, a dozen residential buildings were damaged and one elderly woman was wounded, local officials said.

The southern city of Mykolaiv was subjected to a massive missile strike in the early hours of Sunday as 10 missiles, presumably launched by an S-300 system, hit various parts of town.

Russian officials said on Monday that no clear timeframes have been set for the war in Ukraine, and priority should be given to its efficiency.

"We have no doubts that the special military operation will be completed after all of its objectives are attained. There are no clear timeframes, what counts most is this operation's efficiency," Russian presidential press secretary Dmitry Peskov said as quoted by Russian media.

Officials from the self-proclaimed Donetsk People's Republic claimed on Monday that DPR territory will be liberated from the Ukrainian military this year.

“The liberation of Donbas will be completed this year,” Eduard Basurin, deputy head of the police department of the DPR, said according to Russian media.

-ABC News' Edward Szekeres, Yulia Drozd, and Max Uzol