Frank McKenna, Canada's ambassador to the United States, has resigned.

He informed prime minister-designate Stephen Harper of his decision on Tuesday, Canadian Embassy officials in Washington said Wednesday.

In his two-page letter to Harper, McKenna asked to be relieved of his duty, adding he shared a mutual commitment to Canada with Harper and that he would have had no difficulty working with a Conservative government.

However, "he believes that it would compromise the position of the ambassadorship" were he to stay on, CTV's Joy Malbon -- who obtained a copy of the letter -- said on Newsnet's Mike Duffy Live.

Earlier Wednesday in Washington, McKenna brushed off the question when reporters asked him about his future.

Prime Minister Paul Martin appointed McKenna to the important diplomatic post just less than a year ago.

However, Martin's Liberals were defeated in Monday's election, leading Martin to announce he was quitting as Liberal Party leader.

This started speculation almost immediately that McKenna, a former Liberal premier of New Brunswick, might seek the federal leadership himself.

"I'm not sure he's going to run for the leadership," journalist L. Ian McDonald told Newsnet, noting the Liberal Party is heavily in debt.

"He had a very good commercial law practice in Toronto before. He may want to return to that," McDonald said of McKenna.

In addition, observers say that Harper might have wanted to have his own appointee in Washington in any event, putting McKenna's longer-term future in doubt.

Besides McKenna, some are wondering whether Allan Rock, a former Liberal cabinet minister, is long for his position as Canada's ambassador to the United Nations.

According to a Wednesday report in The Globe and Mail, Rock resisted a pro-Israel shift in policy by Martin, and the Conservatives are likely to be even more pro-Israeli.

Rock himself wanted to seek the Liberal Party's leadership, but he gave up when it became clear Martin had too much of a head start.

In terms of replacing McKenna, McDonald said rumours of former Reform Party leader Preston Manning getting the job were a "non-starter."

Another rumour is that Michael Wilson, finance minister in the Progressive Conservative government of Brian Mulroney, might be a candidate, said CTV's Mike Duffy.

Ontario Premier Dalton McGuinty, a Liberal, said Harper must take care in filling the position, noting that 90 per cent of his province's exports go to the United States.

Text of the letter

The text of Ambassador Frank McKenna's resignation letter to prime minister-designate Stephen Harper, dated Jan. 24:

Dear Mr. Harper,

I want to extend sincere congratulations on your success in today's election.

It was a hard-fought campaign and you have received a very significant vote of confidence from the Canadian public. I know the feeling of exhilaration when the people express confidence in your leadership and vision.

It has been a great privilege for me to serve as Canada's ambassador to the United States throughout the past year. I was most grateful for your personal support and that of your party during my committee hearing on the appointment. It has also been a tremendous personal satisfaction to have been able to serve with the outstanding men and women of this embassy and consulates across the United States of America. Canadians may not fully appreciate the strength and commitment of these dedicated public servants who serve our country so proudly.

I've always placed great value on the importance of the Canada-U.S. relationship, and, in a short period of time, have learned much about how this critical link can be improved and expanded. In that regard, I would be pleased to offer my full co-operation in sharing insights on management of the many significant and crucial issues that we deal with on a daily basis.

However, I believe you would agree that the enormous value of a political appointment to this position is based on the ability to work intimately with the Canadian government. It is this perception of closeness that provides a strong platform for the Canadian ambassador to advance Canada's interest.

While I would have no difficulty working with you or your government, it would be virtually impossible to establish the appearance of total confidence and support in a jurisdiction where political ambassadorial appointees traditionally resign immediately after an election.

Consequently, it is in the best interest of our nation that I submit to you my resignation as Canada's ambassador to the United States. I would be pleased to continue to serve until such time as a replacement is named or, I could depart more expeditiously if it is your wish.

With warmest personal regards and best wishes for a productive mandate.

Sincerely,

Frank McKenna