Zelensky will speak at the Shangri-La Dialogue on Sunday, the International Institute for Strategic Studies said, telling AFP that Zelensky would appear in person.

There had been feverish speculation that Zelensky would make an appearance at this weekend's security forum attended by defence ministers from around the world, including the United States and China.

Zelensky has been touring European nations in recent days to appeal for more military aid for the Ukrainian army, which has been ceding ground to relentless Russian attacks.

The Singapore announcement follows a US decision to partially lift restrictions on using US-provided weapons to strike inside Russia, which Zelensky has hailed as a "step forward".

US President Joe Biden had come under increasing pressure from a desperate Ukraine to ease his ban, but had resisted for fear it could drag NATO into direct conflict or even a nuclear standoff with Moscow.

Germany said Friday it too had given Ukraine permission to fire German-delivered weapons at targets in Russia.

Russian President Vladimir Putin warned Tuesday that there would be "serious consequences" if Western countries give approval to Ukraine.

Ukraine is struggling to hold back a Russian ground offensive in the Kharkiv region, where Moscow recently made its largest territorial gains in 18 months.