Kiev

Russian attacks on Ukraine's Kharkiv region on Sunday killed at least 11 people, said authorities in the border area facing a new offensive by Moscow's forces.

Russian troops since May 10 have carried out a ground assault in the northeastern region, where they have achieved their largest territorial gains in the last 18 months.

Ukrainian President Volodymyr Zelensky said in an exclusive interview with AFP on Friday he expects Russia to step up its offensive in the northeast and warned Kiev only has a quarter of the air defences it needs to hold the front line.

The Ukrainian army said on Thursday it had partially halted a Russian advance in the northeast, where Moscow has secured its largest territorial gains in 18 months over the last week.

Moscow launched a major ground assault across the border into the Kharkiv region last week, a surprise move that has further stretched Ukraine's outgunned and outmanned forces.

Russia said Wednesday its forces had pushed deeper into the Kharkiv region and also captured the symbolic town of Robotyne further south, one of the only prizes of Ukraine's underwhelming counteroffensive last summer.

The United States will back Ukraine until its security is "guaranteed", U.S. Secretary of State Antony Blinken vowed on a trip to Kiev on Tuesday, after Russian forces claimed further advances in the northeastern Kharkiv region.

American military aid for Ukraine is "on its way", U.S. Secretary of State Antony Blinken said in Kiev on Tuesday, as Russia pressed on with a new offensive in the northeastern Kharkiv region.

BELGRADE - Serbian President Aleksandar Vucic met with Ukrainian FM Dmytro Kuleba in Belgrade on Monday to discuss advancement of bilateral relations and the European paths of the two countries.

Russia on Monday pummelled more than 30 towns and villages in Ukraine's northeastern Kharkiv region after launching a surprise ground offensive over the border last week, the local governor said.

The Ukrainian army acknowledged Russia was "achieving tactical success" after the ground assault, which sparked the evacuation of almost 6,000 people.

Ukraine vowed Friday to quash a surprise Russian ground offensive, after troops launched a major cross-border assault in the Kharkiv region, looking to chalk up fresh battlefield gains with Ukraine on the back foot.

South Korean President Yoon Suk Yeol said Thursday that Seoul would keep strong ties with Ukraine and a "smooth" relationship with Russia, while ruling out direct weapon shipments to Kiev.