US President Donald Trump on Saturday directed the Justice Department to investigate Democrats, accusing them of threatening individuals with impeachment and other forms of punishment, without providing evidence to support his allegations.

In a social media post, Trump described the Democrats' actions as a potential "criminal act," accusing them of sending "threatening letters to many people, all innocent."

The move comes after Democratic candidates scored major victories in Tuesday's midterm elections, securing control of Congress from January. Democratic leaders have pledged to intensify congressional oversight of the executive branch through hearings and investigations into the Trump administration's actions.

Democratic lawmakers have recently released copies of letters requesting documents and information on several issues, including donations from technology companies toward a large ballroom Trump is constructing at the White House.

Trump's post also singled out Democratic Senator Elissa Slotkin of Michigan, who said last month that Congress should investigate individuals who have enabled the president's policies.

Speaking at the University of Chicago, Slotkin argued that people considering working for the Trump administration should be aware of potential legal and political consequences.

She said she wanted young people to consider whether joining the administration could expose them to serious problems, describing the message as a deterrent against participating in policies that could later face scrutiny.

Her remarks drew criticism from Republicans. Senator Mike Lee of Utah accused Slotkin of threatening young people seeking careers in public service. Slotkin rejected the accusation, saying Lee had misrepresented her comments and describing the criticism as "manufactured outrage."

The Justice Department has previously investigated Slotkin, a former CIA analyst, alongside other Democratic lawmakers with national security backgrounds.

The investigation followed the lawmakers' release of a video urging members of the military and intelligence community to refuse illegal orders from the Trump administration.

However, a grand jury rejected the effort to indict the lawmakers, dealing a setback to the investigation.

Trump's latest directive raises further questions about the use of federal law enforcement powers against political opponents as Democrats prepare to take control of Congress and expand scrutiny of his administration. (ILKHA)