At least 12 people were killed, including a child, in an attack on Monday by Russian troops on the southern Ukraine city of Mykolaiv, the governor of the Mykolaiv region confirmed.

The attack in Mykolaiv near the Black Sea included the shelling of an oncology hospital, said Vitaliy Kim, governor of the Mykolaiv region. The Ukrainian General Prosecutor's office said 41 people were wounded in the attack, including four children.

Four members of Doctors Without Borders/Medecins Sans Frontieres were at the hospital when it came under attack, said Michel-Oliver Lacharite, head of the group's mission in Ukraine.

"Several explosions took place in close proximity to our staff over the course of about 10 minutes," Lacharite said in a statement. “As they were leaving the area, the MSF team saw injured people and at least one dead body. However, we are not in a position to give exact numbers of dead and injured."

-ABC News' Christine Theodorou

The United States, in coordination with its G-7 and European Union allies, is expected to announce on Wednesday a "sweeping new package of sanctions" that will impose significant costs on Russia and send it further down the road of economic, financial, and technological isolation, sources familiar with the plan told ABC News.

The plan is expected to include a ban on all new investments in Russia, boost sanctions on financial institutions and state-owned enterprises in Russia and impose sanctions on Russian government officials and their family members, the sources said.

The measures are intended to degrade key instruments of Russian state power, impose acute and immediate economic harm on Russia and hold accountable the Russian kleptocracy that funds and supports Russian President Vladimir Putin’s war.

"These measures will be taken in lockstep with our allies and partners, demonstrating our resolve and unity in imposing unprecedented costs on Russia for its war against Ukraine," one of the sources told ABC News.

-ABC News' Molly Nagle

An estimated 11 million people have been evacuated from Ukraine since Russia invaded the country on Feb. 24, the U.N. International Organization on Migration said Tuesday.

The organization also reported that more than 7.1 million people have been displaced within Ukraine as of April 1. That figure comes on top of the one from the U.N. High Commissioner for Refugees showing more than 4 million people have fled abroad.

The International Organization on Migration said more than 2.9 million people still in Ukraine are actively considering "leaving their place of habitual residence due to war."

An ABC News analysis of videos and satellite imagery confirms that some of the bodies seen lying in the streets of Bucha were there as early as March 19, when the Ukrainian city was still occupied by Russian forces, contradicting Russia's claims that the scene was "staged" after its troops left.

As Ukrainian authorities regained control over Bucha, northwest of Kyiv, gruesome images emerged earlier this week showing numerous bodies of dead civilians -- some shot at close range and with their hands bound -- strewn across streets and in mass graves. Russia has denied responsibility, calling the footage "fake" and saying that all of its units withdrew completely from Bucha around March 30.

However, satellite images provided by Maxar Technologies show that at least five of those bodies had been on the street in Bucha since March 19, when Russia said it still occupied the town. ABC News' Visual Verification team compared the satellite imagery to videos of the same scene posted on Twitter by Ukrainian authorities on April 2, as well as footage taken by ABC News journalists in Bucha on April 4.

The satellite imagery of Bucha in March was first reported by The New York Times.

-ABC News' Alice Chambers