Story highlights Warner said he was briefed earlier Sunday

He said he was troubled by the President's Twitter response

Washington (CNN) The top Democrat on the Senate intelligence committee said Sunday morning there was "no specific" threat against the US following attacks Saturday evening in London.

Virginia Sen. Mark Warner, in an interview on CNN's "State of the Union," said that he had been briefed earlier Sunday morning and investigators were still unsure if the attacks were "inspired" or "directed" by militants abroad, like ISIS or al Qaeda.

"There is no specific threat against the United States," Warner added.

On Saturday, masked men wearing fake suicide belts used a van to mow down pedestrians on London Bridge before stabbing people in the nearby Borough Market area.

The attack came about two weeks after a concert bombing in the northern UK city of Manchester.

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