Senior US diplomats have resigned during Donald Trump's first week on the job, creating more high-level openings that the new president must fill.

State Department under secretary for management Patrick Kennedy, a career foreign service officer, planned to retire effective from Friday, the department said.

He was joined by two assistant secretaries, Joyce Barr and Michele Bond, who resigned on Wednesday, and Gentry Smith, who directs the Office of Foreign Missions, is also departing.

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The four join a growing list of long-serving diplomats declining to stay on into the Trump administration.

That list includes Victoria Nuland, assistant secretary for European and Eurasian Affairs, and Gregory Starr, assistant secretary for diplomatic security.

Mr Starr retired on Mr Trump's inauguration day.

Although none of the officials has linked their departure explicitly to Mr Trump, many diplomats have privately expressed concern about serving in his administration, given the unorthodox positions he has taken on many foreign policy issues.

Mr Trump has yet to fill many top diplomatic jobs, including the deputy secretary roles.

His nominee to be secretary of state, Rex Tillerson, is expected to be confirmed by the Senate next week.

Mr Kennedy, relied upon by both Democrats and Republicans, was tapped for the under secretary post in 2007 by George Bush and stayed on throughout Barack Obama's term.

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His position oversees the department's budget and finances, security, global facilities and consular services.

Mr Kennedy, a diplomat since 1973, was criticised for the department's insufficient security at the diplomatic post in Benghazi, Libya, where four Americans were killed in 2012.

In testy congressional hearings he defended then secretary of state Hillary Clinton's handling of the situation and insisted there was no "stand down" order to the US military during the attack,

Bureau records also showed Mr Kennedy asked for the FBI's help in 2015 to change the classification level of an email from Mrs Clinton's private server.

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The FBI ultimately rejected the request.