Democratic presidential candidate Joe Biden has said he is notifying Russia and other foreign governments that he will act aggressively as president to resist any interference in the US elections. The announcement came just hours after Democratic leaders issued a new warning that Congress was targeted by foreign intervention campaign.

Biden said in a statement that he would view foreign interference as an act that significantly affects the relationship between the US and the government of the offending country. 

He criticized President Donald Trump for not accepting enough in response to the US intelligence agency's assessment that Russia interfered in the 2016 presidential election.

Biden said last week he had begun to receive intelligence information and warned that Russia, China and other opponents were trying to undermine the presidential elections. Biden didn’t provide any evidence, but said Russia was still involved in this and that China was also involved in efforts to sow doubt in the US electoral process.

Democratic leaders said in a letter to FBI Director Christopher Wray on Monday that they are concerned that Congress appears to be the target of a concerted foreign intervention campaign to influence the 2020 presidential election.