Vladimir Putin’s proposed cease-fire in Ukraine was over before it started. Ukraine flatly rejected the idea, and reports from the frontline said both sides were firing artillery even after the supposed cease-fire was supposed to start.

Ukrainian leadership and President Joe Biden both think Putin’s cease-fire was a ruse to buy Russia time to reinforce troops and move equipment. Some of the heaviest fighting along the frontlines is in Bakhmut, in eastern Ukraine’s Donetsk region.

Russia started concentrating on the area in August. New satellite imagery from Maxar Technologies showed widespread damage to buildings, homes and infrastructure. It’s a costly campaign for Russia, however, and its military is suffering heavy losses. Ukraine said this week it killed 800 Russians in a single day, and the majority of those casualties were near Bakhmut.

Military analysts were puzzled by Russia’s obsession with Bakhmut, but now there might be an answer.

According to a White House official, Putin ally Yevgeny Prigozhin, the founder of Russia’s powerful private military company The Wagner Group, wants to take over the salt and gypsum mines near Bakhmut. The White House official said there were indications monetary motives were at play.

This isn’t the first time Russian mercenaries stand accused of exploiting natural resources to fund the Russian war machine. The U.S. said Russian mercenaries did the same thing in the Central African Republic, Mali, Sudan and elsewhere.

Wagner’s mercenary force stood at roughly 50,000 before the war started. U.S. intelligence said 4100 Wagner mercenaries died in Ukraine and another 10,000 were wounded. Wagner also recruited from Russian prisons to fill out its ranks. Many of those former felons are now free to return home.

In December, Wagner received a weapons shipment from North Korea, which essentially ensures Putin and Prigozhin’s obsession with Bakhmut will continue for the foreseeable future.

Reuters contributed to this report.