"But it is a necessary struggle. We cannot permit northern Mali to become a safe haven."

Clinton said the availability of weapons was a major problem, describing it as a Pandora's Box that was the "source of one of our biggest threats."

She asserted there was "no doubt that the Algerian terrorists (who attacked the gas facility in In Amenas last week) had weapons from Libya. There's no doubt that the Malian remnants of AQIM have weapons from Libya."

She also singled out the threat from Islamist militants of Boko Haram in northern Nigeria, which according to some counterterrorism officials has begun to establish informal links with AQIM.

Who did Benghazi?

Four months after the Benghazi attack, the official refrain on the search for those responsible was the same.

"We continue to hunt the terrorists responsible for the attacks in Benghazi and are determined to bring them to justice," Clinton said.

Clinton was also cautious in the way she described the attack, citing the unclassified version of the administrative review board she appointed to investigate the attack.

"There's evidence that the attacks were deliberate, opportunistic and pre-coordinated but not necessarily indicative of extensive planning," she said.

Clinton was also asked about a New York Times report Wednesday quoting an Algerian official that some of the attackers on the gas plant last week had also been involved in the Benghazi attack, according to interrogations of the surviving attackers.

Clinton was noncommittal, saying "that would be a new thread." There was no way to confirm the information, and the administration would do everything possible to find out more, she pledged.

Building security

Clinton stressed repeatedly that the United States had to lead the way in providing security assistance in vulnerable nations.

"It's not going to be easy," she said, "because these new countries have no experience with democracy, they don't have any real experience among the leaders in running countries, in doing security."

In Libya, for example, there was willingness to improve security, but no capacity.

"We sent teams out -- both civilian and military -- experts to try to help them. Until recently, while they were going through their transition it was a very difficult conversation, because they didn't have the authority."

She pointed to the example of Colombia, where U.S. assistance over a 10-year period had reduced the threat of terrorist and paramilitary groups.

She also pointed to progress in Somalia, where U.S. funding and training for African troops in the capital and support for the intervention by Kenyan forces had helped push back al-Qaida affiliate al Shabaab.

But "it took time. There were no short cuts," she said.

"We are in for a long-term struggle here and that means we've got to pay attention to places that historically we have chosen not to or had to."