Barack Obama announced a shakeup in his foreign policy team on Wednesday with the unexpected appointment of Susan Rice – known for her support of western intervention in Libya – as his new national security adviser.

As pressure builds on the president to rethink support for ailing rebel groups in Syria, his decision to pick Rice, the US ambassador to the United Nations, will be examined for whether it signals a shift in the administration's foreign policy.

The White House insisted the president's cautious policy on Syria remained unchanged at present but restated its position that all options remained on the table.

In a statement announcing the appointment, Obama said Rice "understands that there is no substitute for American leadership … she is passionate and pragmatic, but mindful that we have to exercise our power wisely."

Rice said her priorities would be to "advance our global leadership and promote the values Americans hold dear".

The appointment will also inflame tensions with Republicans, who blocked earlier attempts to make her secretary of state after controversy over how she handled TV interviews in the aftermath of attacks on US embassy staff in Libya.

The post of national security adviser, currently held by Tom Donilon, is arguably more influential than running the State Department, given its daily access to the president. Furthermore, it does not require confirmation by the Senate, a process which has frustrated many recent White House appointments.

Rice will be replaced in her current role of UN ambassador by national security council official Samantha Power, who will have to face a confirmation process in Senate and is known for her campaigns against genocide.

One of Rice's biggest achievements as US ambassador was pushing through a unanimous security council vote to take "all necessary measures" to protect Libyan civilians.

Her rise was checked, however, by television interviews following the attack on US facilities in Benghazi where she erroneously blamed the incident on spontaneous demonstrations rather than a terrorist attack. The White House insists she was merely representing incomplete CIA assessments at the time.

Many senators who opposed Rice's nomination for secretary of state were due on Wednesday to attend the funeral of Democrat Frank Lautenberg in New York, and the Senate was not sitting. House Republicans have, however, scheduled a hearing on Wednesday morning to discuss the "failure" of Obama's policy of non-intervention in Syria.

Jason Chaffetz, a Republican critic of Rice in the House, was among the first to voice his opposition, tweeting: "Judgment is key to national security matters. That alone should disqualify Susan Rice from her appointment. #benghazi #BadChoice."

Senator John McCain, who led opposition to attempts to nominate Rice for the State Department, said "Obviously I disagree with [her] appointment as national security adviser, but I'll make every effort to work with her on important issues."

The White House acknowledged that Rice had firm views on foreign policy issues, describing her as "smart, experienced and tough".

"The president wants and expects the principals on his team to have strongly held views and express them in meetings with him," said spokesman Jay Carney. "There is always the opportunity when individuals take new roles to further enhance the discussion about foreign policy objectives – the president is always interested in keen discussion."

He stressed that it would be wrong to read too much into the appointments.

"The president's policy on Syria will be the president's policy and is the same as today."

But the White House was on the defensive about its strategy of trying to use peace talks to encourage President Assad to step down, accepting that military setbacks among the rebels could make that more difficult.

"The situation in Syria remains extremely difficult," said Carney. "As the president looks at the options he is mindful of ongoing problems there. We rule out no options."

The White House condemned the assault on the city of Qusair, accusing Syrian government forces of depending "on Hezbollah and Iran to do their work".

"The fact that Assad needs these partners in tyranny says a great deal about how is concerned with his grasp on power not the people he has butchered," said Carney.

He also angrily rejected Republican criticism that Rice had participated in a cover-up over Benghazi, saying it as was a "politically motivated" red herring.

Though Rice's appointment in the face of Republican opposition is a surprise and marks a last-minute addition to Obama's second-term White House line-up, Donilon's departure is less unexpected.

He successfully negotiated the informal summit with Chinese leaders scheduled for this Friday but has served through much of Obama's first term.

The White House said Donilon has sought to stand down after the election but had been asked to stay on by Obama to help with the handover of power in the State Department, Pentagon and CIA.