Washington — Secretary of State Hillary Rodham Clinton faces tough questions in her long-awaited congressional testimony concerning the assault on the U.S. diplomatic mission in Benghazi, Libya, that killed Ambassador Chris Stevens and three other Americans.

Clinton is the sole witness Wednesday at back-to-back hearings before the Senate and House foreign policy panels on the September raid, an independent panel's review that harshly criticised the State Department and the steps the Obama administration is taking to beef up security at U.S. facilities worldwide.

Clinton had been scheduled to testify before Congress last month, but an illness, a concussion and a blood clot near her brain forced her to postpone her appearance.

State Department spokeswoman Victoria Nuland says Secretary Clinton will focus on what U.S. diplomats are doing to put in place recommendations from an Accountability Review Board investigation into the Benghazi attack.

This likely will be Secretary Clinton's last congressional testimony before stepping down as secretary of state.