The House Intelligence Committee will hold its second week of public hearings in the impeachment probe, following testimony by three witnesses last week.

Looking into whether President Donald Trump lied to special counsel Robert Mueller during the Russia probe, a lawyer of the House of Representatives said in court as he requested files from the special counsel's inquiry, "Did the president lie?"

Doug Letter, representing the House Judiciary Committee – which would eventually be responsible for filing articles of impeachment against the president – spoke to the federal appeals court on Monday.

Ahead of the news of this additional thread in the inquiry, Trump tweeted that he is "strongly" considering answering a challenge from opposition Democrats to testify in his own impeachment investigation.  

"Even though I did nothing wrong, and don't like giving credibility to this No Due Process Hoax, I like the idea & will, in order to get Congress focused again, strongly consider it!" Trump tweeted.   

After the speaker of the lower house, Nancy Pelosi, upped the ante by suggesting that Trump come forward to tell the "truth," the Republican president said he was keen. 

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Democrats invite Trump to testify as big impeachment week begins

What's happening this week?

This week, eight individuals are due to testify before House lawmakers as a part of the impeachment proceedings.

Sondland is one of the few individuals who had direct conversations with the president about the Ukraine situation to have cooperated with the inquiry. 

Tim Morrison, a former National Security Council aide, Jennifer Williams, an aide to Vice President Mike Pence, Alexander Vindman, the director for European Affairs at the National Security Council (NSC), and Kurt Volker, the former U.S. special envoy to Ukraine, will speak to the inquiry on Tuesday.

On Wednesday the committee will hear from Sondland, Laura Cooper, a deputy assistant secretary of defense, and David Hale, a State Department official. Fiona Hill, a former top NSC staffer for Europe and Russia, will appear on Thursday.

The timeline for the impeachment process is expected to extend into the new year. Senate Majority Leader Mitch McConnell told reporters in Louisville Monday that he thought the House would be "on this until Christmas."

The U.S. House launched the first public hearing on November 13 of Donald Trump's impeachment investigation, the extraordinary process to determine whether the 45th president of the United States should be removed from office.

(With input from AFP, Reuters)