Bamako - Mali has sent soldiers to reinforce troops expecting an attack by Islamist rebels who have already seized the northern two-thirds of the country, a senior military official close to the defence ministry said on Wednesday.
The deployment was the latest sign of an escalation between government and insurgents who clashed for the first time in about eight months on Monday.
African and Western powers fear the Islamist fighters - some of them allied with al-Qaeda - could use the vast desert zone they took in April as a launching pad for international attacks.
The United Nations has given the green light for an African-led military campaign to retake Mali's north, though logistical and other problems mean that is unlikely to start before September.
"We have deployed technical means and reinforcements to secure the front," the military official told Reuters by telephone, asking not to be named. He did not give details on the numbers of troops.
"We think [the Islamists] want to attack Sevare," he added, referring to a town less than 10km from government-held Mopti - a town close to the rebel frontline.
Malian officials believe the loose coalition of Islamist groups - al-Qaeda in the Islamic Maghreb, Ansar Dine and MUJWA - have moved fighters from their northern desert strongholds of Gao, Kidal and Timbuktu to hit Mopti, where the area's main airport is located.
It was not immediately clear whether the rebels' southward push was an attempt to extend their territory or a show of force ahead of regional peace talks.
Rebel spokespeople have declined to comment on their tactics.
Negotiations between some of the northern rebel groups and the government had been scheduled for Thursday in Ouagadougou, the capital of neighbouring Burkina Faso, but authorities there said on Wednesday they were delayed.
Ansar Dine, one of the main rebel factions, said last week it had ended a ceasefire deal negotiated in December with Mali's government because of the international plans for a military intervention.
Once an example of democracy and development in turbulent West Africa, Mali was plunged into crisis by a March 2012 coup which allowed Tuareg rebels to seize the country's north, demanding an independent homeland.
Islamists who initially fought alongside them soon came to dominate the rebellion. They have since imposed a strict form of shari'ah, or Islamic law, on their territory and destroyed ancient Sufi tombs they see as idolatrous.
Thousands of students in the capital Bamako took to the streets on Wednesday calling for an end to a political crisis caused by the March coup, blocking the city's two main bridges.