US President Joe Biden has signed ratification documents to admit Sweden and Finland to NATO, bringing the northern European countries closer to joining the alliance. 

Biden said the US was the 23rd country to officially approve the two countries' application for membership. The US Senate had overwhelmingly backed the expansion of NATO to include Finland and Sweden in a 95-1 vote last week. 

All 30 NATO allies are expected to approve their applications. Both countries began seeking NATO membership after the Russian invasion of Ukraine earlier this year. 

"Putin thought he could divide us... weaken our resolve. Instead, he's getting exactly what he didn't want. He wanted the Finnishization of NATO, but he is getting the NATOization of Finland together with Sweden," said Biden.