The attack used almost 500 drones and missiles, breaking a record set just days earlier, as Russia tries to overwhelm Ukraine’s air defenses, which shot down most of the weapons.

The warring sides also exchanged prisoners in one of the few results of talks last week, and Russia reported new attacks on the front line.

By Guy Faulconbridge and Lidia Kelly MOSCOW (Reuters) -Russian forces on Wednesday advanced further into Ukraine's northern region of Sumy, threatening the regional capital after taking more than 150 square km (58 sq miles) of the area in less than two weeks,