Energy giant Shell announced Tuesday plans to withdraw from its involvement in all Russian hydrocarbons, including crude oil and natural gas, amid Russia's unprovoked invasion of neighboring Ukraine.

"As an immediate first step, the company will stop all spot purchases of Russian crude oil. It will also shut its service stations, aviation fuels and lubricants operations in Russia," Shell said in a statement.

Shell will immediately stop buying Russian crude oil on the spot market and not renew term contracts. The company will also change its crude oil supply chain to remove Russian volumes, but said "this could take weeks to complete and will lead to reduced throughput at some of our refineries."

In addition, Shell will shut its service stations, aviation fuels and lubricants operations in Russia, and will start a phased withdrawal from Russian petroleum products, pipeline gas and liquefied natural gas.

The company apologized for buying Russian oil last week.

"We are acutely aware that our decision last week to purchase a cargo of Russian crude oil to be refined into products like petrol and diesel -- despite being made with security of supplies at the forefront of our thinking -- was not the right one and we are sorry," Shell CEO Ben van Beurden said in a statement. "As we have already said, we will commit profits from the limited, remaining amounts of Russian oil we will process to a dedicated fund. We will work with aid partners and humanitarian agencies over the coming days and weeks to determine where the monies from this fund are best placed to alleviate the terrible consequences that this war is having on the people of Ukraine."

Ukrainian Foreign Minister Dmytro Kuleba took to Twitter to praise Shell "for taking this moral and responsible step," and he encouraged "other world businesses to follow suit."

At least 21 civilians, including two children, were killed by a Russian airstrike in Ukraine's northeastern city of Sumy on Monday night, according to the regional prosecutor's office.

The strike hit a residential area of Sumy, according to the State Emergency Service of Ukraine, which the regional prosecutor's office said was still on the scene searching for victims Tuesday.

Ukrainian Deputy Prime Minister Iryna Vereshchuk called on Russian forces to maintain the agreed upon temporary cease-fire in Sumy and four other Ukrainian cities to allow civilians to evacuate Tuesday. She said Russian authorities have confirmed to the International Committee of the Red Cross that one evacuation route out of Sumy will be open, but Ukrainian officials are awaiting confirmation on the other routes they submitted.

-ABC News' Julia Drozd and Patrick Reevell

More than 2 million people have been forced to flee Ukraine since Russian forces invaded on Feb. 24, according to the latest figures from the United Nations High Commissioner for Refugees (UNHCR).

Over 1.2 million of the refugees from Ukraine are in neighboring Poland, UNHCR figures show.

"Today the outflow of refugees from Ukraine reaches two million people. Two million," U.N. High Commissioner for Refugees Filippo Grandi said Tuesday in a post on his official Twitter account.

-ABC News' Zoe Magee

Russia declared Tuesday a temporary cease-fire in five besieged cities of Ukraine, including the capital, to let civilians leave.

"For safe evacuation of civilians from populated areas, a cease-fire is declared and humanitarian corridors are opening from Kyiv, Chernihiv, Sumy, Kharkiv, and Mariupol from 10:00 a.m. today," Russian Ministry of Defense spokesman Igor Konashenkov said at a press briefing.

All five cities except Kyiv had sustained brutal, indiscriminate bombardment in recent days.

It's the fourth attempt to hold fire and allow civilians to escape the onslaught since Russian forces invaded Ukraine on Feb. 24. Russian and Ukrainian negotiators have been holding talks in recent days, and the Russian delegation has previously agreed to a temporary cease-fire and opening of humanitarian corridors in parts of Ukraine. But Russia has violated its own cease-fire and shelled evacuation points, while falsely accusing Ukraine of using people as human shields.

The hard-hit cities of Kharkiv and Mariupol were reported to be quiet Tuesday morning, with a local official telling ABC News that the center of Mariupol, a strategic port in the southeast, is not being shelled for the first time in days.

Ukraine said Russia has agreed this time to allow civilians to evacuate not only to Russia but also to other parts of Ukraine. Columns of buses and trucks with humanitarian aid are currently headed to Sumy, Mariupol and possibly other cities.

Ukrainian Deputy Prime Minister Iryna Vereshchuk said Russia has confirmed to the International Committee of the Red Cross that one route out of Sumy will be open. Vereshchuk said she hopes Russia will confirm routes for the other cities and also for the eastern city of Volnovakha. She warned Ukraine has information that Russia may have plans to disrupt the evacuations by leading civilians out of the agreed safe routes, in order to claim that Ukraine is not observing the agreement.

Petro Andrushenko, advisor to the mayor of Mariupol, said the city plans to evacuate people as long as Russian forces do not fire. A column of 60 buses and nine trucks of medical aid and food are headed to Mariupol now, and the hope is that at least 4,000 people can be evacuated via the buses plus an unknown number of private cars that will join the convoy, according to Andrushenko.

"If Russia doesn’t break it, we plan to evacuate people," Andrushenko told ABC News via telephone Tuesday morning.

-ABC News' Julia Drozd and Patrick Reevell