WASHINGTON (REUTERS) - At least four senior US State Department officials are departing their posts by Friday (Jan 27), a senior department official told Reuters, leaving vacancies at top policy-making and management levels.

Republican President Donald Trump's nominee for Secretary of State, former Exxon Mobil Corp chairman Rex Tillerson, was approved by the Senate foreign relations committee.

Tillerson, who has yet to be confirmed by the full Senate, will be under more pressure to fill these senior positions.

The departures were discussed at State Department Thursday morning meetings and a statement said all politically-appointed officers were asked to submit letters of resignation by the outgoing administration of Democrat Barack Obama in coordination with Trump's.

"Of the officers whose resignations were accepted, some will continue in the Foreign Service in other positions and others will retire by choice or because they have exceeded the time limits of their grade in service," said a statement by acting State Department spokesman Mark Toner.

Among those whom Reuters has confirmed are leaving, are Gregory Starr, Assistant Secretary for State for Diplomatic Security and Michele Bond, Assistant Secretary for Consular Affairs.

Thomas Countryman, the acting undersecretary for arms control and international security, was asked to leave by Friday, US officials said, as was Patrick Kennedy, under secretary of state for management.

"This is not unusual, it's not a mass protest or a show of indignation," said one senior US official.

Some of those asked to leave by Friday at 5 pm were prepared to stay on "and do their jobs" until replacements were confirmed, said one of the US officials.