Pro-Russian separatist fighters in eastern Ukraine are receiving new armored vehicles and fighters trained in Russia, and plan to launch a major counteroffensive against government forces, a rebel leader said in a video released on Saturday.

The four-month conflict in eastern Ukraine has reached a critical phase, with Kiev and Western governments watching nervously to see if Russia will intervene in support of the increasingly besieged rebels — an intention that Moscow denies.

Alexander Zakharchenko, prime minister of the self-proclaimed "Donetsk People's Republic," said the rebels were in the process of receiving some 150 armored vehicles, including 30 tanks, as well as 1,200 fighters who he said had spent four months training in Russia.