France is expected to more than triple its troop numbers in Mali as raids continue on Islamist insurgents following overnight air strikes on a small town that had been seized by the rebels.

Sources close to the French defence minister said the number of French troops deployed in the west African country would "gradually" reach 2,500. There are currently 800 French troops in Mali, with hundreds more on the way over the next few days.

France carried out a fifth day of air strikes in a vast desert area seized last year by an Islamist alliance, which combines al-Qaida's north African wing, AQIM, with Mali's home-grown Movement for Oneness and Jihad in West Africa (Mojwa) and Ansar Dine rebel groups.

In a news conference in the United Arab Emirates, the French president, Franç ois Hollande said France had three aims: to stop the rebel advances, to secure the capital, Bamako, and to help the Mali government regain control of the whole country.

He said France would take a lesser role "as soon as there is an African force, in coming days or weeks", adding that France did not intend to stay.

Hollande said: "France should only intervene in Africa in exceptional circumstances and for a limited time. That's what we will do." In response to questions about a return to France's controversial role in its former colonies, he said the Mali intervention, in an international legal framework with UN backing, had nothing to do with the practices of "a bygone era".

But he added that France's role was to ensure that "when we end our intervention, Mali is safe, has legitimate authorities, an electoral process and there are no more terrorists threatening its territory".

Commentators in France said this would imply a drawn-out presence in the poor west African country, which is in political disarray following a coup last year and the fall of the desert north to Islamist groups, who operate a drug trafficking and kidnap economy in northern Mali and other Sahelian countries.

Asked what France intended to do with the insurgents, Hollande said: "Destroy them. Take them captive, if possible."

West African defence chiefs were meeting in Bamako to approve plans to speed up the deployment of 3,300 regional troops, foreseen in a UN-backed intervention plan to be led by Africans. African troops are expected to begin to be deployed within a week. Troops from the Ecowas grouping of west African states are expected to bolster the dishevelled Malian army.

A convoy of 40 to 50 armed trucks carrying French troops crossed into Mali on Tuesday from Ivory Coast, where they were stationed.

The UN refugee agency said the military clashes in northern Mali were adding to the already large numbers of people who had fled its recent conflicts.

The agency spokesman, Adrian Edwards, said 1,230 refugees from Mali had arrived in Niger, Burkina Faso and Mauritania as a result of recent clashes between the French-backed Malian army and the rebel groups.

More than 144,000 Malian refugees fled to neighbouring countries in 2012, while nearly 200,000 people fled their homes in northern Mali and were displaced within the country.

French raids took place overnight over the town of Diabaly, 220 miles (350km) from the capital, Bamako.

The French foreign minister, Laurent Fabius – accompanying Hollande on the Dubai visit aimed at firming up trade relations and making progress on a possible sale of 60 Rafale fighter jets – said he was confident Gulf Arab states would also help the Mali campaign.

Fabius said there would be a meeting of donors for the Mali operation, most likely in Addis Ababa at the end of January.

He predicted the current level of the French involvement in Mali would go on for "a matter of weeks".

But a Mojwa commander taunted the French, telling Associated Press: "I would advise France not to sing their victory song too quickly. They managed to leave Afghanistan. They will never leave Mali."

Oumar Ould Hamaha said: "It's to our advantage that they send in French troops on foot. We are waiting for them. And what they should know is that every French soldier that comes into our territory should make sure to prepare his will beforehand, because he will not leave alive."

In Lisbon, the US defence secretary, Leon Panetta, said no American troops would be put on the ground in Mali. The US is providing intelligence-gathering assistance to the French, and officials would not rule out having American aircraft land there to provide airlift and logistical support. Panetta said the US was still working through the details of assistance it would provide France.

The Ecowas mission head in Bamako, Aboudou Toure Cheaka, said west African troops would be on the ground within a week. Their immediate mission would be to help stop the rebel advance, while preparations for a full intervention continued, he said.

The original timetable for the 3,300-strong UN-sanctioned African force – backed by western logistics, money and intelligence services – did not initially foresee full deployment before September due to logistical constraints.

Senegal, Burkina Faso, Niger, Nigeria and Guinea have all offered troops. But the regional powerhouse, Nigeria, which is due to lead the mission, has cautioned that even if some troops arrive in Mali soon, training will take time.

The plan is being fast-tracked following a plea for help by Mali's government after mobile columns of Islamist fighters last week threatened the central garrison towns of Mopti and Sevare, with its key airport.

The French prime minister, Jean-Marc Ayrault, said France's goals were to stop the Islamist rebels, to "safeguard the existence of Mali" and pave the way for the African-led military operation.

French intervention has raised the risk for eight French hostages held by al-Qaida allies in the Sahara and for 30,000 French expatriates living in neighbouring states. Concerned about reprisals at home, France has tightened security at public buildings and on public transport.

The Mali government contradicted other reports that the Islamists who seized control of Diabali – a town in the government-controlled south – had entered the country from Mauritania.

"The people in Diabali are bandits who fled there from the north," said Manga Dembele, the minister of communication, in an interview with the Guardian at the government headquarters in Bamako. "They have come to seek refuge in the town and they are hiding in the population."

But relations with Mauritania to Mali's west and Algeria to the north have been fraught in recent months, with accusations that both countries have harboured Islamists who crossed over porous desert borders from Mali to stock up on fuel and other supplies.

"We are not worried that the Islamists will arrive in Bamako," said Dembele.

Responding to questions about the apparent lack of security in the capital where government offices and ministries have little security and are accessible to members of the public. Dembele said the situation in the city was under control.

Dembele sought to calm increasing anxiety in Bamako about the existence of Islamist "sleeper cells", which it is feared could launch an attack on the city in response to the mounting campaign against them in the north.