Vadym Skibitsky, Ukraine’s deputy military intelligence chief, said the recruits would take part in attacks over the spring and summer in the east and south of the country.
Currently, Ukrainian officials have reported that there were 280,000 Russian ground troops deployed in the country.
“We expect them to conduct offensives in Donetsk and Kharkiv regions, as well as possibly Zaporizhzhia but to defend in Kherson and Crimea, this is the number of men they will need for such a task,” Mr Skibitsky said when asked to explain why they expect such a surge of troops.
“If Russia loses this time around, then Putin will collapse.”
Mr Skibitsky said the last wave of mobilisation will take place on January 15 following the holiday period as Russia tries to “overwhelm” Ukraine with a large mass of troops.
Russia has denied it is preparing a second wave of mobilisation with Vladimir Putin calling it “pointless” last month.
The Kremlin called for a 36-hour truce on Friday in keeping with Russian Orthodox holiday.
Ukraine rejected the truce, however, which Volodymyr Zelensky described as "cover to at least briefly stop the advance of our guys in Donbas and bring equipment, ammunition and mobilised men closer to our positions".
Ukraine also claimed that Russian troops continued to attack during the ceasefire, with an emergency worker killed by shelling in Kherson and reports of artillery fire in the Donbas city of Kramatorsk.
Air raid alerts were issued in multiple Ukrainian cities, but no explosions were reported.
In its latest update, however, the Ministry of Defence said that fighting between Russian and Ukrainian forces has continued at a “routine level” despite the ceasefire.
In its daily intelligence update, the MoD said that in the fiercely contested area around Kremina town in eastern Ukraine’s Luhansk province, fighting was focused in heavily forested terrain to the town’s west, where “combat has devolved to dismounted infantry fighting, often at short range”.
The MoD said: “Fighting has continued at a routine level into the Orthodox Christmas period. One of the most fiercely contested sectors continues to be around the town of Kremina, in Luhansk Oblast.
“In the last three weeks, the fighting around Kremina has focused on the heavily forested terrain to the west of the town.
“With the coniferous woodland providing some cover from air observation even in winter, both sides are highly likely struggling to accurately adjust artillery fire.”