The battle for control of northern Mali appears to be drawing nearer to the capital, Bamako, as a growing alliance of international forces continued to attack Islamist strongholds.

Banamba, a town only 90 miles (145km) from Bamako, was put on alert after jihadists were reportedly seen in the area. The Malian army was reported to have deployed 100 soldiers to the town, with reinforcements on the way.

There are reports that the threat to the town is connected to the attack on Diabaly, a small garrison town 250 miles north-east of Bamako that was taken by rebels earlier this week. Soldiers and at least one civilian were injured in the attack. Phone lines within the town have now been cut, making communication almost impossible.

An official in Banamba told Associated Press yesterday that reports had been received of rebels leaving Diabaly for Banamba. "We don't have a [military] base here, we have no defences. So the military has come to secure the town," he said. "From Monday to today, no jihadists have entered our town. But there are reports that a column [of rebel vehicles] was seen heading toward us from Diabaly."

The threat to Banamba comes amid increasing concern about the threat from rebel fighters in government-held southern Mali. The Guardian has learned – in a claim that cannot be verified – that three armed men were arrested in Bamako on Wednesday after being seen by residents travelling in a taxi with guns.

An official from Mali's National Commission of Human Rights (CNDH) said the men were detained at a market and taken by the Sécurité d'État, Mali's state security service, to an unknown location.

"It is very difficult to know exactly what is going on, because normal measures have been suspended under the current state of emergency," said Amadou Bocar Teguete. "But we know that these men were armed and arrested at the Dgikoraone market on suspicion of involvement in terrorism."

The arrests coincide with claims that Islamist sleeper cells are active in Bamako and could plot attacks in retaliation for the international military intervention to oust Islamists. The hostage crisis in Algeria is also being claimed as a revenge attack.

France has been increasing its role in the fighting, which is expected ultimately to involve 2,500 troops. Air strikes since last Friday have failed to oust rebels from Konna, the town 430 miles from Bamako whose capture initially prompted the French intervention. There have been reports of fresh fighting between Islamists and Malian soldiers there.

The French defence minister, Jean-Yves le Drian, said France had increased its number of troops in Mali to 1,400.

"The actions of French forces, be it air forces or ground forces, are ongoing," Le Drian said in Paris. "They took place yesterday, they took place last night, they took place today, they will take place tomorrow."

After European Union foreign ministers met in Brussels, their Malian counterpart, Tieman Hubert Coulibaly, said "the entire international community" had to be mobilised to help Mali and the region.

"What is happening in Mali is a global threat," Coulibaly said at a press conference. "Remember what happened on September 11," he said, referring to the 2001 terrorist attacks in the US. "It is that terrorism can happen anywhere, at any moment, to anyone."

The military action is being bolstered by a contingent of almost 200 Nigerian soldiers, who flew in on Thursday from Kaduna in northern Nigeria, and 2,000 soldiers from Chad, who are due to arrive in Mali shortly.

A source in Mopti, a town on the front between Islamist and government-held territory, which has a nearby army base at Sévaré, said the area was being heavily patrolled by French and Malian soldiers.

"There are French tanks and many Malian soldiers in Sévaré," said Issa Ballo. "Earlier, local people saw three French tanks heading in the direction of Konna.

"The army is moving around on pickups and motorbikes, they are checking everything in Mopti, and arresting anyone they think is suspicious and putting them inside military vehicles."