President Trump speaks to the staff at the Department of Homeland Security on Jan. 25. (AFP)

President Trump on Thursday intensified his criticism of the decision to commute the sentence of military leaker Chelsea Manning, calling her a “traitor” who should remain in prison.

In a tweet, Trump claimed Manning had called former president Barack Obama a “weak leader” even after her 35-year sentence was commuted in the last days of the Obama administration.

Trump appeared to be referring to a column that Manning wrote in the Guardian newspaper. In the commentary, she argued that Obama's legacy will leave “few permanent accomplishments” because he often sought common ground and compromise rather than battling harder against “unparalleled resistance from his opponents.”

Manning wrote: “What we need is an unapologetic progressive leader.”

The use of the word “traitor” is often tossed around by political leaders and others to describe alleged acts that threaten national security. But it is rare for a president to brand someone as a traitor, and Trump's comment raised questions about whether he could try to bring further action against Manning, who is scheduled to be released in May.

“Ungrateful TRAITOR Chelsea Manning, who should never have been released from prison, is now calling President Obama a weak leader. Terrible!” Trump wrote.

Last week, days before being named White House spokesman, Sean Spicer said Trump was “troubled” by Obama’s commutation of the sentence of Manning, an Army private convicted of taking troves of secret diplomatic and military documents and disclosing them to WikiLeaks.

“It’s disappointing, and it sends a very troubling message when it comes to the handling of classified information and to the consequences of those who leak information that threatens the security of our nation,” Spicer told reporters.

Chelsea Manning was convicted in 2013 for leaking secret diplomatic and military documents to WikiLeaks. Former president Barack Obama commuted her 35-year sentence in the last days of his term. (Thomas Johnson,Gillian Brockell/The Washington Post)

Spicer called Manning “someone who has given away this country’s secrets,” but he did not directly answer a question about whether Trump would take any steps to reverse or delay Obama’s decision.

Obama said that the seven years Manning has served behind bars amounted to enough punishment and that she had been given an excessive sentence.

Manning, then known as Bradley Manning, was arrested in Iraq in May 2010 after trasmitting documents to WikiLeaks that came to be known as the Iraq and Afghanistan “War Logs.” Manning also shared a video that showed a U.S. Apache helicopter in Baghdad opening fire on a group of people that the crew believed to be insurgents. Among the dead were two journalists who worked for the Reuters news agency. Manning also leaked documents pertaining to Guantanamo Bay prisoners, as well as 250,000 State Department cables.

Manning came out as transgender after her conviction.