Official Says Commander of Group That Massacred 21 in Tunisia Is Dead

TUNIS — Tunisian security forces have killed the commander of the group responsible for the recent massacre of 21 foreign tourists at the National Bardo Museum, Tunisia’s prime minister, Habib Essid, announced on Sunday.

The commander, Khaled Chayeb, also known as Lokman Abu Sakhr, was killed with eight other Islamist militants by members of the national guard in an ambush in southern Tunisia overnight, the interior minister, Najem Gharsalli, later told journalists in a news briefing.

The news came as the Tunisian government hosted several foreign leaders, including President François Hollande of France and President Mahmoud Abbas of the Palestinian Authority, at a march against terrorism. The dignitaries joined thousands of Tunisians, waving red national flags and banners denouncing terrorism, who proceeded across town to the site of the March 18 massacre.

As the ceremonies here unfolded, the French authorities announced that a fourth French tourist had died from wounds suffered in the attack, bringing the death toll to 21.

A Tunisian policeman was also killed, and 42 people, mostly tourists visiting the museum, were wounded.

The mass shooting was one of the worst terrorist attacks in Tunisia in more than a decade, and it has raised fears that Islamist extremists are set on undermining the tentative gains the country has made since the Arab Spring revolt that overthrew the dictatorship of President Zine el-Abidine Ben Ali four years ago.

Mr. Gharsalli laid the blame for the attack on the Okba Ibn Nafaa brigade, an Islamist group linked to Al Qaeda that has been lodged in the Chaambi Mountains on the Algerian-Tunisian border for the past few years.

Mr. Chayeb was the leader of the group, which has concentrated on attacking army and national guard forces in the western border region and has ties to a network of underground cells around the country.

The group is allied to the larger North African Islamist movement, Al Qaeda in the Islamic Maghreb, and Ansar al-Shariah in Tunisia, both of which are led by men who were direct disciples of Osama bin Laden and who are now based in Libya. Libya, an increasingly lawless state, has allowed militant groups to recruit and train members almost unimpeded in recent months.

Members of Okba Ibn Nafaa posted a video online soon after the Bardo attack giving an account of the assault and the two gunmen who carried it out. The Islamic State has praised the attack, although terrorism experts and government officials have concluded that its pronouncements are closer to a blessing than a direct claim of responsibility.

Besides the nine militants killed overnight, the government said it had detained 23 people involved in the museum attack, including one woman. The man named as the organizer of the assault, Mohamed Amine Guebli, is among those under arrest. Maher Ben Mouldi Kaidi, a Tunisian accused of providing the weapons to the gunmen near the museum, remains a fugitive, as are two Moroccans and an Algerian, Mr. Gharsalli said.

The two gunmen had recently undergone training in Libya, along with Mr. Kaidi, the interior minister said on Thursday at a news conference. Two others of the group had taken part in fighting in Syria, he said.