Satellite imagery has detected another mass grave outside Mariupol, the besieged strategic port city in southeast Ukraine that's been bombarded by Russian forces for weeks, Radio Free Europe first reported on Monday.

Driving the news: The third mass grave site detected by U.S. firm Planet Labs' satellite imagery around Mariupol was captured from March 24 to April 24 in the Russian-occupied village of Staryi Krym, some five miles from the city, according to dates on the images and local officials.

• The images show the grave site to have expanded from around 200 feet long on March 24 to about 650 feet last Sunday, Mariupol City Council officials noted in a Telegram post on Tuesday.
• Earlier satellite imagery has also indicated mass grave sites in the Mariupol-area villages of Vynohradne and Manhush, along with the Kyiv region city of Bucha.

What they're saying: Mariupol Mayor Vadym Boychenko, told Radio Free Europe the imagery concurs with Ukrainian officials' information indicating that Russian forces have "used mass graves to bury civilians killed" in the bombardment of the city, according to a Washington Post translation of the article.

• The information indicated this sometimes involved "enlisting residents in the digging work in exchange for food," Boychenko said.

The big picture: The Kremlin has repeatedly denied targeting civilians or other war crimes. The International Criminal Court and other prosecutorial agencies have opened investigations into allegations that Russian forces have committed these and other crimes against humanity.

• United Nations human rights chief Michelle Bachelet said last week that the U.N. was seeing growing evidence of war crimes in Ukraine while cataloging a "horror story" of violations perpetrated against civilians.

Go deeper: What counts as a war crime and why they're so hard to prosecute

Editor's note: This article has been updated with comment Boychenko and further context.