The US Department of Justice will investigate whether FBI agents spied on President Donald Trump’s 2016 election campaign for “inappropriate purposes”.
In a tweet, Mr Trump said he wanted to know whether his predecessor’s administration ordered such a move.
The call comes after US media reports suggesting the FBI had an informant meeting campaign aides.
US Deputy Attorney-General Rod Rosenstein said action would be taken if any infiltration was found.
“If anyone did infiltrate or surveil participants in a presidential campaign for inappropriate purposes, we need to know about it and take appropriate action,” Mr Rosenstein said in a statement.
What is the scope of the investigation?
There is already an investigation into all aspects relating to Mr Trump’s campaign for the 2016 election and whether Russia tried to influence the outcome.
Mr Trump’s latest demand came amid a series of tweets on Sunday denouncing a “witch hunt” that, he said, had found no collusion by his campaign with Russia.
This refers to the ongoing investigation led by Special Counsel Robert Mueller into Russia’s efforts to interfere in the 2016 US election, whether there was any collusion between the Kremlin and Mr Trump’s election campaign and whether the president tried unlawfully to obstruct the inquiry.
Mr Trump has constantly attacked the inquiry.