Chad's new ruling junta has vowed to root out a rebel leader it accuses of "war crimes", after the country's 30-year president Idriss Deby Itno died in combat with his forces last week.
The Front for Change and Concord in Chad (FACT) is the largest of several armed rebel groups with rear bases across the border in Libya or Sudan.
Here is a snapshot:
- FACT -
FACT emerged in April 2016 from a split in the Union for Democracy and Development (UFDD) group, led by Deby's former defence minister, Mahamat Nouri.
As with many rebel groups before it, FACT's stomping ground is northern Chad, a vast, restive and lawless desert region abandoned to illegal gold miners and gangs of traffickers.
Its base, though, is in the Fezzan region of southern Libya, where it has a deal with Khalifa Haftar, the military strongman of the country's east.
According to the UN, FACT fighters have been used to protect forces affiliated to Haftar as well as certain oil installations.
Their leader is Mahamat Mahadi Ali, who once lived in France, where he was previously a member of the Socialist Party.
He was a leader in the 1990s of the biggest rebel group at the time, the Movement for Democracy and Justice in Chad (MDJT).
He is a Goran, a clan of the ethnic Toubou community.
FACT launched a major incursion on April 11, the day of the election in which President Idriss Deby Itno secured a sixth term.
According to the army, several columns of heavily armed vehicles rolled in from Libya, attacking a customs post at the border in the province of Tibesti, some 1,000 kilometres (600 miles) from the capital.
Deby, who himself came to power in 1990 at the head of a rebel force which rolled into the capital, went to the region to lead the fighting. According to the authorities, he died on April 19 from combat injuries.
Experts believe FACT has between 1,500 and 2,000 fighters.
The Chadian army claim to have killed several hundred last week and taken nearly 250 prisoner.
- Other groups -
Among other groups, the biggest is the Union of Resistance Forces (UFR), an alliance created in 2009 from 10 rebel groups.
Its fighters are mainly members of the Zaghawa ethnic group, from which Deby hailed, and are led by Deby's nephew, Timan Erdimi, who fled to Qatar for a decade after falling into disgrace.
In 2019, the UFR mounted an attempt to oust Deby by sending a column of fighters in pickup trucks from Libya via Sudan.
They were beaten back by French air strikes, requested by Deby, a major ally in France's anti-jihadist campaign in the Sahel.
On April 18, the UFR gave its verbal support to FACT.
Another group, also based on the Chad-Libya border, is the Military Command Council for the Salvation of the Republic, or CCMSR.
Created in 2016, the CCMSR launched an assault on Kouri Bougoudi in the gold-rich Tibesti region in northern Chad, triggering a violent response from the armed forces.
Its operational capacity fell back sharply after that, with splits and desertions in its ranks, according to a recent UN assessment.
In March, the CCMSR allied with three other rebel groups, including the National Front for Democracy and Justice (FNDJT) led by Abakar Tollimi.
Chad has been the theatre of coups and attempted coups since it gained independence from France in 1960.
Deby himself took power after mounting an attack on the capital N'Djamena from Sudan in 1990.