WASHINGTON: President Barack Obama nominated a new ambassador to Libya on Wednesday, filling a post that has been vacant since Chris Stevens was killed in the Sept. 11 Benghazi attack and signaling the United States' commitment to the North African country as it undergoes a perilous transition from decades of dictatorship.

The announcement came as Secretary of State John Kerry was meeting Libyan Prime Minister Ali Zidan, and two days after the six-month anniversary of the storming of the U.S. diplomatic mission in the eastern Libyan city. No one has yet been captured for the attack, which has caused significant political headaches for Obama and his foreign policy team.

"The United States will continue to stand with Libya during this difficult time of transition," Kerry told reporters. "The Libyan people have begun to chart the course for their own future, and they're defining it. Obviously there are challenges ahead and we understand that, from building political consensus to strengthening the security and protecting human rights, and growing the Libyan economy."

Kerry thanked the Libyan government for its cooperation after the Benghazi attack and insisted that "those who killed Americans in Benghazi will be brought to justice." He promised Zidan that America would continue working for a stable Libya.

"We must not walk away from the difficult work that Chris Stevens and his cohorts were so dedicated to," Kerry said. Stevens was the first ambassador killed in the line of duty since the U.S. ambassador to Afghanistan in 1979.

To replace Stevens, the White House tapped Deborah K. Jones, a career diplomat who has served in Kuwait, United Arab Emirates and the now-shuttered U.S. Embassy in Syria. Jones, who currently works as a scholar at the Middle East Institute in Washington, also has spent time at embassies in Turkey and Ethiopia.

Jones will assume a difficult position heading the embassy in Libya's capital, Tripoli. The North African country has been beset by lawlessness, militant group rivalries and political instability since rebels, with the help of the U.S. and other governments, overthrew long-time dictator Moammar Gadhafi in 2011.

"She is a very capable and experienced diplomat," Kerry said of Jones. "I have no doubt that she will help to strengthen the partnership between us."

Zidan also met with Obama and his national security adviser Tom Donilon at the White House.

The president added his support Libya's democratic efforts and outlined areas the U.S. could help the government strengthen its institutions and improve the rule of law, according to a statement by Caitlin Hayden, spokeswoman for the National Security Council.

From Washington's perspective, the most pressing problem is insecurity.

Stevens and three other Americans were killed a half-year ago when a large group of men, possibly tied to Islamic extremist groups, assaulted the American outpost in Benghazi, and the help that arrived proved far too little and too late.

The militant group Ansar Al-Shariah is suspected of carrying out the attack, which the administration initially attributed to a protest over an American-made, anti-Islam video that spiraled out of control. Officials later retracted that account and called it a terror attack. But no one has been punished in Libya or elsewhere for involvement.

Zidan has been trying to reassert government control over Libya. Last month, he called on militias to evacuate buildings and headquarters and join government security forces, vowing that his government will take a hardline stand against any armed group that tries to hijack control of "Tripoli or Benghazi or any other city."

However, the Libyan government heavily depends on security provided by commanders of several powerful militias that the president has labeled "legitimate" forces. Militias in Libya often act with impunity, running their own prison cells, making arrests and taking confessions in total absence of state control and oversight.

The lawlessness also has allowed Gadhafi's once-vast stock of weapons to fall into the hands of extremists who've sparked a civil war in neighboring Mali. A France-led intervention has pushed back the Islamist militants after they seized half the country last year.

Speaking next to Kerry, Zidan thanked Obama and the U.S. for its key contribution in the effort to defeat Gadhafi. He said Libya would partner the U.S. in stabilizing his country and region.

"This relationship will be at the best level," Zidan, in his first to trip to Washington as prime minister, said through an interpreter.