WASHINGTON, Dec. 17 (Xinhua) -- U.S. President Donald Trump said on Sunday that he is not considering firing special counsel Robert Mueller.

Mueller is investigating allegations of Russian interference in the last year's U.S. presidential election and collusion between the Trump campaign and Moscow.

When asked if he was considering dismissing Mueller, Trump responded, "No, I'm not," and did not elaborate on the issue.

Democratic lawmakers have raised concern that Trump might fire Mueller.

The president, however, criticized the fact that Mueller's team had gained access to tens of thousands of emails sent and received by officials from Trump's transition team before the start of the presidency.

Trump said it was "not looking good."

Mueller's team received those emails from the General Services Administration that had housed Trump's transition team.

In a letter to several congressional panels Saturday, a lawyer for the transition accused Mueller of illegally obtaining the emails.

In response, a spokesman for Mueller said the emails were obtained appropriately.

Mueller's probe entered a new phase earlier this month when former National Security Adviser Michael Flynn pleaded guilty to lying to the FBI about his contacts with Russia.

Flynn is now cooperating with Mueller over the investigation.

Russia has denied meddling in the election, while Trump has denied any collusion.