Ukraine has accused Russia of attacking the besieged city of Bakhmut with phosphorus munitions.
Prigozhin said they would leave on May 10 because of heavy losses and inadequate ammunition supplies.
Russia has launched a series of missiles at Ukrainian cities in the second pre-dawn attack in three days.
Ten days after leaked Pentagon documents burst into public view, what have we learned about the war in Ukraine?
The US believes the UN Secretary General is too willing to accommodate Russian interests, according to fresh revelations in classified documents leaked online.
What to make of the dozens of classified American Defence Department documents - maps, charts and photographs - now circulating on the internet?
Russia has taken the presidency of the UN Security Council despite Ukraine urging members to block the move.
Beijing has portrayed itself as a potential peacemaker on Ukraine, but its close relationship with Moscow has been on display during visit.