American authorities are on the hunt for a serial bomber after suspicious packages targeting leading Democrats and others were discovered in what was dubbed an act of “terrorism”.

Basic explosive devices described as “pipe bombs” were sent to the homes of former president Barack Obama, former secretary of state Hillary Clinton and the New York headquarters of broadcaster CNN.

The three bombs followed the discovery of a similar device at the residence of George Soros, the billionaire philanthropist and prominent donor to liberal causes, on Monday.

On Wednesday night more suspicious packages were being investigated near offices of Democratic politicians including Debbie Wasserman Schultz, the former head of the Democratic National Committee. Two packages were also sent to California Congresswoman Maxine Waters, the FBI said.

Police officers said they were investigating whether an individual or a group of people were behind the apparent attempts to take life, warning that other packages may still be undiscovered.