Tunisian authorities yesterday were investigating the disappearance of 33 residents from the same town after families reported they had left overnight to join Islamic State militants in Libya, locals said.

Tunisian militants make up one of the largest groups of foreign fighters in Islamic State ranks, but the departure of such a large number from the same town illustrates the struggle the Tunisian government is facing as it struggles to control jihadist recruiters and their followers.

The interior ministry said yesterday it was investigating the disappearance of the group, from Remada, a small central town of 11,000 near the border with Libya. Most of the ‘missing’ residents were conservative salafists, but the group also included a pilot, two soldiers and one female civilian, officials and local residents added.

“The town is really in shock,” said Mbarka, a resident who said a number of families related to those involved had received messages from their relatives saying they had left for Libya. The gunman who carried out last month’s deadly shooting at Tunisia’s Sousse beach resort, where 38 foreign tourists died, and the militants involved in the Bardo museum attack in March, were radicalised in Tunisia and trained in jihadist camps in Libya before returning.

Islamic State is making inroads in Libya, where two rival governments and their armed forces are battling for control, leaving a security vacuum that has allowed Islamist militants and migrant smugglers to expand their operations.

Meanwhile, Tunisian air force planes yesterday were searching for the group of Tunisian civilians along the Libya border area. Residents said the group, which includes several teenagers, had left after a meeting at the local mosque.

Tunisian militants make up one of the largest groups of foreign fighters in Islamic State ranks

Worried about a flow of militants across its border, Tunisia says it has started building a wall and trench along 168 kilometres of its Libya frontier. The dividing wall will be ready by the end of 2015, the government said.

Since its 2011 revolution against Zine El-Abidine Ben Ali, Tunisia has enjoyed a mostly peaceful transition to democracy.

However, one of the Arab region’s most secular countries, Tunisia has also struggled with the rise of ultra-conservative Islamist groups, some of them violent.

Authorities say they are cracking down on illegal mosques and those preaching extremist messages since the Sousse attack, the worst militant assault in the country’s modern history.

Faten Abd Elhak, fiancée of the pilot who disappeared, said he had taken part in bombardments against militant camps in the mountains in the past. But he had become disillusioned with the armed forces and wanted to leave, she said.

“It’s true his brother was an extremist who didn’t hide his desire to join Islamic State, but he himself was not an extremist,” she said. “They have all left for Libya, some of them might want to join Islamic State, but not him.”