DONETSK, Ukraine (AP) — Ukraine's rebels are surrounded and ready to agree to a cease-fire to prevent a "humanitarian catastrophe," the insurgents' new leader said Saturday as conditions deteriorated in the rebel stronghold of Donetsk, artillery thundering through deserted streets.

There was no immediate government response to the cease-fire statement. The government has made steady advances against the rebels in recent weeks.

"We are prepared to stop firing to bar the spread of the scale of the humanitarian catastrophe in Donbass (eastern Ukraine)," Aleksandr Zakharchenko, the so-called prime minister of the Donetsk separatists, said in a statement on a rebel website.