Belmokhtar remains at large and the US is offering a $5m (£3.2m) reward for information leading to his arrest.
Three US citizens were among at least 37 hostages killed when Algerian troops stormed the Tigantourine plant.
Days earlier, gunmen had seized local and foreign workers at the complex.
"Belmokhtar brought terror and blood to these innocent people and now we intend to bring Belmokhtar to justice," said Preet Bharara, US attorney for the Southern District of New York, in a statement.
- Fought Soviet forces in Afghanistan in late 1980s
- Former leading figure in Al-Qaeda in the Islamic Maghreb (AQIM). Left in late 2012 after falling out with leaders
- Leader of a group known variously as the Signed-in-Blood Battalion, the Masked Men Brigade and the Khaled Abu al-Abbas Brigade
- Known as "The One-Eyed" as he often wears an eyepatch over a lost eye
- French intelligence dubbed him "The Uncatchable", while locals refer to him as "Mr Marlboro" for his illicit cigarette operation
Belmokhtar is a former leading figure in al-Qaeda in the Islamic Maghreb (AQIM) but is now believed to head a group of militants known variously as the Signed-in-Blood Battalion, the Masked Men Brigade and the Khaled Abu al-Abbas Brigade.
He was designated a foreign terrorist by the US Treasury Department in 2003.
The hostage crisis began on 16 January when militants attacked two buses carrying foreign workers from the Tigantourine gas facility near In Amenas in eastern Algeria.
The militants took foreign workers hostage at the gas complex, which was quickly surrounded by the Algerian army. Special forces stormed the living area on 19 January and the gas treatment plant two days later.
At least 29 militants also died in the shoot-out.