Russia's Defence Ministry says its troops will hold their fire and open evacuation routes for civilians trying to flee from danger in four Ukrainian cities.

The ministry said the ceasefire starts at 9:00 a.m. Monday, local time, in the capital Kyiv, the second-largest city Kharkiv, Mariupol in the east and Sumy in the northeast.

Residents will make their way out of the cities on foot or using land transportation before being airlifted. The Russian military says it will use drones to monitor the evacuations.

The ministry said the ceasefire is being implemented in response to a request from French President Emmanuel Macron to Russian President Vladimir Putin.

Ukrainian Defence Minister Oleksii Reznikov said the government is doing all it can to open the routes.

The announcement came as Russian forces intensify their offensive, having shelled a research installation that handles nuclear materials in Kharkiv.

Ukraine and Russia have previously agreed on two ceasefires to allow residents to leave Mariupol. But the agreements fell through.

Each side blames the other for the failed attempts.

The number of evacuees is likely to be the largest since the Russian invasion began.

It remains to be seen whether the latest announcement will result in circumstances that allow people to make their way to safety.