Ukrainian President Volodymyr Zelensky on Friday hailed the United States' decision to allow Kyiv to use American-supplied weapons to strike in Russia, with some restrictions.

"This is a step forward toward (the) goal ... of making it possible to defend our people who live in the villages on the border," Zelensky told reporters in Stockholm where he took part in a Ukraine-Northern Europe security summit.

US officials said Thursday that President Joe Biden had secretly lifted restrictions on Ukraine using certain American-supplied weapons against targets inside Russian territory, but only to defend the under-fire Kharkiv region.

Biden had come under increasing pressure from a desperate Ukraine to ease his ban, but had so far resisted amid fears it could drag NATO into direct conflict or even a nuclear standoff with Moscow.

The Kremlin accused the West on Thursday of "entering a new round of escalations in tensions".