Mozambican forces clashed with suspected Islamist insurgents who staged their closest attack yet to a Total SE liquefied natural gas project since Islamic State began claiming responsibility for violence in the region last year, according to three people familiar with the matter.

The assault began in the early hours of Tuesday morning in the town of Monjane, about 5 kilometers (3 miles) south of the perimeter fence of Total’s $20 billion project, according to the people who didn’t want to be named because they’re not authorized to talk to the press. The development is Africa’s biggest private investment.

Total is closely monitoring the situation in the area, and remains in constant contact with the government about it, the company said in an emailed response to questions.

Mozambique last week said its security forces repelled an attack by insurgents on the town of Mute about 21 kilometers south of the project. It was the second raid on the town in the northern Cabo Delgado province this month.

The latest attack increases fears that the insurgents, who locals refer to as al Shabaab but who aren’t aligned with the Somali group of the same name, may target the LNG project.

In August, fighters seized the port town of Mocimboa da Praia, about 42 kilometers south of Mute, raising the stakes in a conflict that’s killed about 2,500 people and caused 570,000 to flee their homes since it started three years ago.

Mozambique’s government has struggled to contain the insurgency and President Filipe Nyusi has faced criticism for refusing outside help. Leaders from the Southern African Development Community are set to meet in January to agree on a plan to prevent the conflict from spilling across Mozambique’s borders.