Ashton Carter was confirmed as US secretary of defense Thursday, taking on the job of supervising the war against Islamic State jihadists in the final two years of Barack Obama's presidency.

The Senate -- by a vote of 93 to five -- easily confirmed Carter, an accomplished defense technocrat, to replace Chuck Hagel as head of the Pentagon.

Despite deep divisions between the White House and many Republicans over foreign and US military policy, Carter's nomination encountered negligible resistance and he sailed through the confirmation process with bipartisan support.

"I think Dr. Carter will be a good secretary of defense," but "I must candidly express concern about the task that faces Dr. Carter, and the limited influence he may have," hawkish Senator John McCain said.

McCain for months has complained bitterly about the White House's "over-centralization of foreign and defense policies," arguing that Obama's tight hold on the reins hamstrings Pentagon chiefs as they oversee military operations.

"We need a coherent national security strategy," McCain added.

Hagel resigned under pressure, criticized by some as too passive in the face of rapidly changing security developments, and as the United States prepares its next phase in the war against Islamic extremists.

With Obama this week sending his request to Congress for a new authorization for use of military force against the jihadists, Carter will serve a high-profile role of focusing and carrying out US strategy in the turbulent conflict as lawmakers hash out the limits to the war powers they will grant the president.