The elusive jihadist who staged a deadly siege of an Algerian gas plant a year ago, Moktar Belmokhtar, has the means to stage a similar attack, a top US general said Thursday.

Belmokhtar was the mastermind behind an assault on a remote gas facility near In Amenas on January 16 last year that left 38 hostages dead, following a three-day siege and rescue attempt.

"We still believe he has the capability to do another attack like In Amenas," General David Rodriguez, head of the US Africa Command, told reporters.

The United States in December designated Belmokhtar's group, "Signatories in Blood," as a terrorist organization, and the State Department is offering a $5 million reward for information leading to the Algerian's capture.

The one-eyed Islamist is the former leader of Al-Qaeda in the Islamic Maghreb (AQIM) and is also believed to be behind twin car bombings in Niger in May that left at least 20 people dead.

Belmokhtar is "in the middle of the Sahel," exploiting the porous borders and isolated terrain between southwest Libya and northeastern Mali, according to Rodriguez.

He said the US government was trying to help Libya and other countries in the region bolster security and counter the threat posed by extremists.

"We're working with Libya to start to improve their effort to handle their security," the four-star general said.

"We're also working with the French at the opposite end of that challenge in Mali where we continue to provide airlift and intelligence support to their efforts there," he said.

The Algeria siege by Belmokhtar's group was said to have been carried out in retaliation for France's military intervention against Islamist militants in Mali.

The US general also said Washington was encouraging governments in Niger and Chad "to help limit freedom of movement" for Islamist militants.

To assist Tripoli control its borders and improve security, the US military is preparing to conduct a 24-week training course for "5,000 to 8,000" Libyan forces, with tentative plans to launch the effort in mid-2014, he said.

The training project is part of a NATO mission approved last year, with Britain, Italy, Turkey and Morrocco also taking part.

But logistical and financial hurdles have delayed the effort, and Libyan authorities have struggled to provide a sufficient number of recruits for the training, Rodriguez said.

Turkish trainers "didn't get nearly as many recruits as they wanted" for the program, he said.

Libya's new government is struggling to restore order and build up a professional police force and army in a country awash with weapons and well-armed militias since the overthrow of Muammar Gaddafi in 2011.