WARSAW: US President Joe Biden on Wednesday called Russia’s suspension of a nuclear treaty a “big mistake” as Moscow sought closer ties to China and said it was fighting for “historical” lands in Ukraine.

Biden spoke before meeting NATO chief Jens Stoltenberg and eastern European leaders in a bid to shore up support for Kyiv nearly a year after Russia invaded Ukraine.

Asked by a journalist for a reaction to Russia’s decision, Biden at first joked in Warsaw that he didn’t “have time”, then said: “big mistake”. The leaders of Bulgaria, the Czech Republic, Estonia, Hungary, Latvia, Lithuania, Poland, Romania and Slovakia attended the talks with Biden in Warsaw amid widespread concern in their countries that the conflict could spill over.

Stoltenberg urged allies to “step up our support for Ukraine” saying that “we cannot allow Russia to continue to chip away at European security”. In Moscow, President Vladimir Putin attended a patriotic rally, telling a crowd of tens of thousands that Russia was fighting “for our historical lands, for our people”.

Earlier, he held talks with China’s top diplomat Wang Yi, who was visiting Moscow after Washington and NATO voiced concern that China could be preparing to supply Russia with weapons to pursue its war in Ukraine.