Prime Minister Shinzo Abe said today three citizens of Japan were killed when gunmen stormed Tunisia's national museum, with his government dismissing earlier reports of five Japanese deaths "an error".

"At the moment, we know three Japanese nationals are dead and three injured," Abe told reporters. "No matter what the reasons were, terrorism can never be forgiven. We strongly condemn this," he said, adding that Tokyo was still working to collect information. "We will exert the utmost effort in our fight against terrorism by deepening cooperation with the international community."

Attackers opened fire at a major museum in Tunisia's capital on Wednesday, gunning down 17 tourists as dozens more sprinted to safety. At least 22 people in all were killed, including two gunmen, but some attackers may have escaped, authorities said.

Tunisian Prime Minister Habib Essid had earlier said 21 people were killed: 17 tourists, two gunmen, a Tunisian security officer and a Tunisian cleaning woman. He said the dead tourists came from Italy, Poland, Germany and Spain. Tunisian authorities later raised the death toll to 22 but did not provide the nationality of the latest victim.