Ukrainian President Volodymyr Zelenskyy claimed during his nightly address Wednesday that several settlements have been recaptured from Russia in the Kharkiv region, though did not provide further details.

"There is good news from the Kharkiv region. However, now is not the time to name the liberated settlements," he said.

-ABC News' Jason Volack and Max Uzol

Ukrainian President Volodymyr Zelenskyy said Tuesday he was the first foreign leader to have a conversation with new United Kingdom Prime Minister Liz Truss.

Zelenskyy said in a statement on social media that he invited her to Ukraine and the two discussed security guarantees and "coordinated further pressure" on Russia.

"The goal is to stop the aggression & bring the perpetrators to justice," he said.

A Downing Street spokeswoman said in a statement that Truss reiterated the U.K.'s "steadfast support" for Ukraine in her first call with a foreign leader since taking office.

“The leaders discussed the need to strengthen global security and the measures necessary to cut off the funds fueling Putin’s war machine," the statement said.

"She praised the Ukrainians' fight for sovereignty and self-determination and said it was essential Ukraine succeeds and Russia fails," the statement continued, adding that Truss was "delighted to accept an invitation to visit President Zelenskyy in Ukraine soon."

-ABC News' Rashid Haddou

More than 1,000 children have been confirmed killed or injured in Ukraine since Russia invaded six months ago, the humanitarian organization Save the Children said Tuesday.

At least 372 children have been killed and 635 children injured since Feb. 24 -- for an average of five children killed or injured each day, according to a Save the Children analysis of verified United Nations data.

"This grim milestone marks another dark day in this senseless war. Innocent children are being injured and killed nearly every day in Ukraine," Sonia Khush, Save the Children's country director in Ukraine, said in a statement. "Ruthless violence, including the use of explosive weapons in urban areas, has taken a big toll on children over the past six months."

"Our teams inside Ukraine continue to witness the devastating impact this war is having on children and families who have endured more than eight years of conflict. The world must act now," the statement continued.

The number of civilian casualties in the war is likely "considerably" higher, the U.N. said.

The nuclear watchdog of the United Nations is calling for the immediate establishment of a "nuclear safety and security protection zone" around the Russian-occupied Zaporizhzhia nuclear power plant in southeastern Ukraine.

The recommendation, among several others, was made in a second report released Tuesday by the International Atomic Energy Agency, which deployed an expert mission to the besieged plant last week.

"The IAEA recommends that shelling on site and in its vicinity should be stopped immediately to avoid any further damages to the plant and associated facilities, for the safety of the operating staff and to maintain the physical integrity to support safe and secure operation," the agency wrote in the report. "This requires agreement by all relevant parties to the establishment of a nuclear safety and security protection zone around the ZNPP."

The Zaporizhzhia nuclear power plant is the largest in Ukraine and all of Europe. Invading Russian forces overran the site and the surrounding town of Enerhodar in early March. The Ukrainian workers have been left in place to keep the plant operating, as it supplies electricity across the war-torn country, but the site is now on the front line between Russian-occupied and Ukrainian-controlled territory. Moscow and Kyiv have traded blame for shelling at or near the plant in recent days and weeks, fueling fears that the conflict could spark a radiation disaster.

The IAEA said it aims to maintain a "continued presence" at the plant to "help further improve and deepen the understanding of the situation."

"While the ongoing shelling has not yet triggered a nuclear emergency, it continues to represent a constant threat to nuclear safety and security with potential impact on critical safety functions that may lead to radiological consequences with great safety significance," the agency wrote in the latest report.

U.S. President Joe Biden made an unannounced visit to war-torn Ukraine on Monday, arriving in Kyiv as Washington signals its ongoing support ahead of the one-year anniversary of Russia's invasion.

Biden's visit came ahead of a planned meeting with NATO allies in Poland. He is expected to give a speech at the Royal Castle Arcades in Warsaw on Tuesday evening to offer an appraisal of international support during the first year of the war and to address "how we will continue to stand with the people of Ukraine for as long as it takes," White House spokesperson Karine Jean-Pierre said in a statement earlier this month.

Biden also plans to meet in Poland with leaders of the Bucharest Nine, a group of eastern NATO allies formed in 2015 in response to Russia's annexation of Ukraine's Crimean Peninsula.

Ukrainian President Volodymyr Zelenskyy made a dramatic visit to the United States in December, his first known international trip since the Russian invasion began in February 2022. Zelenskyy met with Biden at the White House in Washington, D.C., before addressing members of U.S. Congress on Capitol Hill.