Such letters should accordingly open with an apology, or at least an expression of regret, when an apology is really unnecessary.

回信的时候应当先对所提出的异议表示道歉，确实不需要道歉时，起码也得表示遗憾。

youdao

The chief executive of Seattle, Washington, and the governor of Maryland issued letters of apology to China.

FORBES: Fact and Comment

Mr Parris's news conferences comes after the Chief Constable of South Wales Police, Sir Anthony Burden, sent letters of apology earlier this week to him and four other men, who were charged with the murder following the original investigation in 1988.

BBC: Lynette murder - inquiry call

No cumbersome exchange of letters - within 24 hours or so I had my reply, explanation and apology - see above - by dealing with the council itself rather than through an intermediary.

BBC: Lines painted in early Spring...