At least three civilians were killed and 16 others wounded Tuesday by Russian shelling in Kharkiv, Ukraine's second-largest city, according to the regional governor.

Kharkiv Oblast Gov. Oleg Sinegubov said Russian forces were using multiple-launch rocket systems on the northeastern city from a roughly 25-mile distance.

-ABC News' Iryna Hnatiuk

The Russian Ministry of Defense claimed Tuesday that a temporary cease-fire has been declared in the besieged city of Mariupol and that a humanitarian corridor has been opened to allow Ukrainian fighters to lay down their arms escape with their lives.

But Russian officials earlier stated that the Ukrainian fighters taking a stand at the Azovstal Iron and Steel Works plant in Mariupol had until 4 p.m. local time to surrender, a deadline that has now passed.

"For this purpose, a 'complete silence regime' has been introduced, any hostilities have been stopped, units of the Russian Armed Forces and the formations of the Donetsk People's Republic along the entire perimeter of Azovstal have been withdrawn to a safe distance," said Mikhail Mizintsev, head of the Russian National Defense Control Center.

Mizintsev said that the humanitarian corridor was opened "in view of the catastrophic situation at the Azovstal metallurgical plant in the city of Mariupol, and also guided by purely humane principles."

Ukrainian officials have not confirmed the opening of the humanitarian corridor out of Mariupol. Ukrainian Deputy Prime Minister Iryna Vereshchuk said earlier that humanitarian corridors would not be reopened on Tuesday.

Mizintsev said three humanitarian convoys have been set up in the immediate vicinity of the plant to take evacuees in three directions.

"Each humanitarian convoy includes 30 buses and vehicles for transporting people, 10 ambulances with medical and nursing teams," Mizintsev said. "In addition, meeting points and temporary accommodation have been deployed in all three directions, food points and primary medical care have been organized."

Russia is starting the next phase of its "special military operation" in neighboring Ukraine, according to Russian Foreign Minister Sergey Lavrov.

"This operation will continue. Another stage of this operation is beginning," Lavrov said in an interview Tuesday with English-language Indian television network India Today. "I am sure this will be a very important moment of this entire special operation."

Lavrov noted that the goal of the operation is to "fully liberate" the Russian-backed separatist regions of eastern Ukraine's Donetsk and Luhansk oblasts, "as it was declared from the very start."

Russia-backed separatist forces are trying to storm a steel plant in besieged Mariupol where Ukrainian troops are holed up, according to separatist spokesperson Eduard Basurin.

Basurin, spokesman of the militia for a pro-Russia breakaway republic of Donetsk in eastern Ukraine's disputed Donbas region, told Russian state media on Tuesday that a separatist special forces unit was chosen to assist the Russian military in storming the giant plant of the Azovstal Iron and Steel Works company in Mariupol, a strategic port city in eastern Ukraine's war-torn Donetsk Oblast that has been under heavy Russian bombardment since the start of the invasion on Feb. 24.

Basurin said they have already started their operation at the Azovstal plant, with Russian forces providing air and artillery support.

The territory of the Azovstal plant is the last holdout for the Ukrainian resistance in Mariupol, as Russian forces accelerate their efforts to capture city. The Mariupol City Council has previously said there are at least 1,000 people, including Ukrainian troops, on the grounds of the plant. Ukrainian Deputy Prime Minister Iryna Vereshchuk said Monday that civilians, including women and children, are also sheltering there and she called for an "urgent humanitarian corridor" to allow them to evacuate.

The Ukrainian government did not immediately confirm Tuesday that Russian forces are storming the Azovstal plant.

-ABC News' Yulia Drozd

At least one person -- a journalist -- was killed in a rocket attack on a residential building in Kyiv on Thursday evening, ABC News has learned.

Kyiv Mayor Vitali Kilitschko said Friday that rescuers had found the body of a victim amid the rubble.

Radio Liberty, a service of the U.S.-funded Radio Free Europe/Radio Liberty, reported that one of its employees, Vira Gyrych, was killed when a Russian missile hit her apartment in the Ukrainian capital on Thursday. Her body was found beneath the wreckage Friday morning, according to the report.

Gyrych had worked as a journalist and producer for Radio Liberty's Kyiv bureau since 2018. Prior to that, she worked for leading Ukrainian television channels, according to Radio Liberty.

"The editorial staff of Radio Liberty expresses its condolences to the family of Vira Gyrych and will remember her as a bright and kind person, a true professional," Radio Liberty said in its report.

Israeli Ambassador to Ukraine Michael Brodsky also confirmed Gyrych's death in a Twitter post, saying she was a former employee of the Israeli embassy in Kyiv.

Thursday's rocket attack came as United Nations Secretary-General Antonio Guterres visited Kyiv. Five Russian missiles flew into the city, according to Ukrainian President Volodymyr Zelenskyy. At least 10 people were injured, including four who were hospitalized, according to the Kyiv City Council.