The US Department of State has said they are not familiar with the letters sent by six Congressmen to US President Joe Biden and Secretary of State Antony Blinken but noted that they usually respond confidentially.

"I'm not familiar with the letter. We generally don't comment on letters that we get from members of Congress," said Matthew Miller, spokesperson for the US Department of State, at a regular briefing in Washington yesterday.

He said they usually respond to such letters confidentially but will continue to make known privately as well as publicly any concerns that they have.