President Donald Trump attacked the FBI and lawmakers probing suspected Russian meddling in the 2016 US presidential election, drawing sharp criticism for saying an excessive focus on Russia led investigators to miss signs that could have prevented a deadly school shooting in Florida.

In a series of tweets over the weekend from his Mar-a-Lago estate in Florida, Trump said congressional investigations and political "hatred" showed Russia had succeeded in sowing "discord, disruption and chaos" in the United States.

He accused his Democratic predecessor, Barack Obama, of failing to do enough to stop Russian election interference.