Malian soldiers have fired on Islamist fighters in the centre of the country, military sources say.
Details remain sketchy but some sources say the Islamists, who last year seized a vast area of the north, have advanced towards Mopti - the last town under government control.
The army responded with “warning shots”, military sources say.
In December, the UN approved an African-led military operation against the Islamist groups.
Last week, one of the Islamist groups, Ansar Dine, said it was ending the ceasefire it had previously announced during talks with mediators.