Militant Islamists and Tuareg-led rebels have clashed in northern Mali.
The rebels said they launched an offensive against the Movement for Unity and Jihad in West Africa (Mujao) group, but they were later repelled, AFP news agency reported.
Meanwhile, rebels and another Islamist group, Ansar Dine, held talks in neighbouring Burkina Faso.
The Islamists said they were ready to work with the Malian government to end months of instability in the north.
The UN Security Council is due to discuss plans in the next few weeks to deploy a regional force to northern Mali.
The regional body, the Economic Community of West African States (Ecowas), says it will send about 3,300 troops to Mali, if the UN gives the green light.
'Strangling the rebels'
The Islamists and rebels - a secular group made up of ethnic Tuaregs known as the National Movement for the Liberation of Azawad (MNLA) - captured northern Mali earlier this year following a joint offensive against government forces.
However, their alliance has since collapsed, with the Islamists taking territory from the MNLA.
MNLA spokesman Moussa Ag Assarid told AFP their offensive on Friday was aimed at capturing their former stronghold of Gao from Mujao.
Mujao spokesman Oumar Ould Hamaha confirmed that they had been attacked, and at least 12 of their fighters had been captured, AP news agency reports.
Mr Hamaha said Mujao fought back.
"We burned their vehicles.... We are in the process of strangling them," he is quoted as saying.
AFP quoted unnamed security sources as saying the MNLA had suffered a "heavy defeat".
In Burkina Faso, representatives of Ansar Dine - Mujao's Islamist rivals - and the MNLA issued a joint statement saying they were prepared to "engage resolutely in a process of political dialogue" to end instability in Mali.
This followed talks with mediator Blaise Compaore, the president of Burkina Faso who is leading mediation efforts on behalf of Ecowas.
Ecowas officials have previously said they would send a force to northern Mali only if talks fail.
Mali's President Amadou Toumani Toure was overthrown in March by a junta of disaffected soldiers who claimed his government had not dealt effectively with a Tuareg rebellion that had started in January.
Islamist groups - who have since fallen out with their Tuareg allies - took advantage of the ensuing chaos and seized all the region's major towns, including the historic city of Timbuktu.
The Islamists have destroyed ancient shrines in Timbuktu and have imposed a strict version of Islamic law, sparking international outrage.