Russia battles Ukrainian troops for a third day after major incursion

Russian forces were battling Ukrainian troops for a third day on Thursday after they smashed through the Russian border in the Kursk region, an audacious attack on the world's biggest nuclear power that has forced Moscow to call in reserves.

In one of the biggest Ukrainian attacks on Russia of the two-year war, around 1,000 Ukrainian troops rammed through the Russian border in the early hours of Aug. 6 with tanks and armoured vehicles, covered in the air by swarms of drones and pounding artillery, according to Russian officials.

Ukrainian forces swept through the fields and forests of the border towards the north of the border town of Sudzha, the last operational trans-shipping point for Russian natural gas to Europe via Ukraine.

President Vladimir Putin cast the attack as a "major provocation". The White House said the United States, opens new tab - Ukraine's biggest backer - had no prior knowledge of the attack and would seek more details from Kyiv.