Algeria will never succumb to terrorism or allow al Qaeda to establish a "Sahelistan" power base in arid northwest Africa, Sellal told a news conference in Algiers, Reuters reported.
"There is clear political will," the prime minister said.
Sellal said a Canadian citizen whom he named only as Chedad, a surname found among Arabs in the region, was among 29 gunmen killed and had "coordinated" the attack. Another three militants were taken alive and were in custody.
Among hostages confirmed dead by their own governments were three Americans, seven Japanese, six Filipinos and three Britons; others from Britain, Norway and elsewhere were listed as unaccounted for. Sellal said seven of the 37 foreign dead were unidentified, while a further five foreigners were missing.
The U.S. State Department said Monday the Americans killed were Victor Lynn Lovelady, Gordon Lee Rowan and Frederick Buttaccio. Buttaccio was identified as a Houston resident, and Lovelady hailed from Nederland, Texas, according to the Associated Press. A hometown for Rowan was not released.
Nearly 700 Algerians and 100 other foreigners survived.
An Algerian security source told Reuters investigators suspect that the attackers had inside help to map the complex and gain entry, and were were questioning at least two employees.
As Algerian forces combed the Tigantourine plant near the town of In Amenas for explosives and the missing, survivors and the bereaved told tales of terror, narrow escapes and of death.
"The terrorists lined up four hostages and assassinated them ... shot them in the head," a brother of Kenneth Whiteside told Sky News, in an account of the Briton's death given to the family by an Algerian colleague who witnessed it. "Kenny just smiled the whole way through. He'd accepted his fate."
Filipino survivor Joseph Balmaceda said gunmen used him for cover: "Whenever government troops tried to use a helicopter to shoot at the enemy, we were used as human shields."
Another Briton, Garry Barlow, called his wife from within the site before he was killed and said: "I'm sat here at my desk with Semtex strapped to my chest," Reuters reported.
Several hostages died on Thursday when Algerian helicopters blasted jeeps in which the militants were trying to move them.
An Algerian security source had earlier told Reuters that documents found on the bodies of two militants had identified them as Canadians: "A Canadian was among the militants. He was coordinating the attack," Sellal said.
In Ottawa, Canada's foreign affairs department said it was seeking information. Security experts noted that some Canadian citizens had been involved with international militants before.
Sellal said 29 terrorists were killed during assaults by Algerian military forces to end the four-day standoff and "a few" may have escaped after having used hostages as shields from the Algerian military. Sellal said the terrorists came from Egypt, Canada, Mali, Niger, Mauritania and Tunisia, and that three were captured.
Algerian special forces stormed the plant on Saturday to end the siege, moving in to head off what government officials said was a plot by the terrorists to blow up the complex and kill all their hostages with mines sown throughout the site.
On Sunday, Algerian bomb squads sent in to blow up or defuse the explosives found 25 bodies, said a security official, who spoke on condition of anonymity because of the sensitivity of the situation.
"These bodies are difficult to identify. They could be the bodies of foreign hostages or Algerians or terrorists," the official said.
Special forces continue to secure the facility and look for more victims, said Algerian spokesman Mohamed Said.
The plant was a joint venture operated by British firm BP, Statoil of Norway and Sonatrach of Algeria. Hundreds of workers were employed at the plant, including many foreigners.