Chad's transitional authorities and rebel groups signed a peace agreement in Doha on Monday ahead of a broad national reconciliation dialogue to take place later this month.

A signing ceremony for the agreement, which included the parties agreeing to take part in a national, inclusive dialogue, was attended by more than 30 rebel groups and followed months of talks in the Qatari capital.

Details, such as how the deal will be implemented and how adherence to it will be monitored, were not immediately released.

Mahamat Zene Cherif, the interim military government's foreign minister, told reporters he believed the agreement would lead to sustainable peace in Chad, adding that 1,500 representatives would attend the national dialogue on August 20.

The national dialogue is meant to include a wide range of groups and parties as well as the government and the rebels.

"Most of the armed groups signed this agreement and they will take part in the national dialogue. And this national, inclusive dialogue is a forum for all Chadian people," he said, brushing off concerns that not all groups had signed up to the deal.

The Front for Change and Concord in Chad (FACT), a Libya-based rebel group that threatened to march on the capital last year, quickly rejected the Doha agreement on Sunday.

FACT said in a statement the deal had failed to adequately consider its demands, which included release of prisoners captured during the fighting. The group said it remained open to further discussion.

A source familiar with the agreement said those who had signed had agreed to a permanent ceasefire and to work towards civilian disarmament.

Chad's interim military government had also committed to not launching military or police operations in neighbouring countries against groups who had signed up to the deal, the source said, speaking on condition of anonymity.

The interim military government is headed by Mahamat Idriss Deby, who last year seized power following the death of his father, responsibility for which was claimed by FACT.

Deby declared himself head of a Transitional Military Council in April 2021 after his father, longtime ruler Idriss Deby, was killed while visiting troops fighting the rebel insurgency in the north.

Initially, his council said it would oversee an 18-month transition to democratic rule, but it has shown little sign of organising elections as that deadline has neared.

Qatar's foreign minister, Sheikh Mohammed bin Abdulrahman Al-Thani, speaking at the signing, called on groups that had not signed to join the agreement.

Wealthy Gulf state Qatar, an ally of the United States, facilitated the negotiations.