A series of satellite images show what appears to be a growing mass grave site on the outskirts of Mariupol, the southern port city where Ukrainian officials say tens of thousands have been killed during a two-month long siege by Russian forces.

An analysis of the images by The New York Times shows approximately 300 pits dug close to a cemetery in Manhush, a village about nine miles west of Mariupol. The holes were dug over two weeks between March and April, while Russian forces were in control of the town, according to a Times analysis.

The first rows of pits appeared in images captured between March 23 and March 26. Satellite images captured two weeks later, on April 6, show a dramatic expansion of the site, with more than 200 freshly dug holes encompassing nearly an acre of land. Each pit shows dimensions of about 6 by 10 feet.

“These are huge graves, and they were dug for our dead civilians from Mariupol,” said Pyotr Andryushchenko, an aide to Mariupol’s mayor who released the coordinates for the site in a Telegram post on Thursday. “You can see from the images how big this area is — these graves are not meant for a small village like Manhush.”