French troops pressed northward in Mali territory occupied by radical Islamists on Wednesday, launching a land assault which will put soldiers in direct combat "in 1 to 72 hours," military officials said.

A trickle of refugees left on foot from Diabaly, a town seized two days ago by the jihadists who have held onto it despite a punishing bombing campaign by French fighter jets. According to residents, the refugees arrived in Niono town, 70 kilometers away.

French ground operations began overnight, France's military chief of staff Adm. Edouard Guillaud, said on Europe 1 television Wednesday. He stressed that French infantry units "will be fighting directly in coming hours, but I am unable to say whether it is in one hour or in 72 hours.… Of course, we will be fighting directly."

• Map: Conflict in Mali

Armoured vehicles loaded with French troops were seen heading toward Niono. The natural target for the French infantry is Diabaly, located 400 kilometers northeast of the capital and roughly 70 kilometers north of Niono. French warplanes have carried out airstrikes on Diabaly since the weekend, when a column of dozens of rebel vehicles cut off the road to Diabaly and seized the town as well as its military camp.

Ibrahim Komnotogo, a resident of Diabaly who heads a USAID-financed rice agriculture project, happened to be outside the town when the jihadists encircled it. He has 20 employees and contractors who he says are stuck inside the town, which has a population of 35,000. He told The Associated Press that al-Qaeda-linked rebels have sealed off the roads and were preventing people from leaving. He was last able to speak to his employees on Tuesday, and had not had news of them since, after the telephone network was cut.

Komnotogo says he fears the Islamists are planning to hide within Diabaly's mud-walled neighborhoods and use the population as a human shield.

Military camp bombed

"The jihadists have split up. They don't move around in big groups … they are out in the streets, in fours, and fives and sixes, and they are living inside the most populated neighbourhoods," he said, explaining that they had taken over the homes of people who managed to flee before the road was cut off.

French warplanes bombarded the military camp, but there have been no airstrikes inside the actual town, which begins at the eastern wall of the garrison. Residents have evacuated the neighborhood called Bordeaux, after its sister city in France, which is only 500 metres from the camp, he said. They have moved mostly into a quarter called Berlin, about 1 kilometre from the military installation.

"They are preventing the population from leaving. We have been trying to get our employees out, but they can't leave," said Komnotogo. "They have parked their pickup trucks inside the courtyards of empty homes. They have beards. And they wear boubous (a flowing robe). No one approaches them. Everyone is afraid," he said.

However some people succeeded in leaving Diabaly and later arrived in Niono, indicating that some were slipping through the rebels' noose, or that the fighters had decided to allow residents to leave.

Tidiane Diarra, one of Komnotogo's employees, who distributes water to rice cultivators, arrived in Niono on Wednesday. He said he had heard that the Islamists were blocking the way out of the town, but could not confirm it because he lives in a village 4 kilometres outside of Diabaly. From there, no one stopped him from leaving.

• 9 questions about the Mali conflict

The fighters, he said, are going to be difficult for the French to weed out, because they are now travelling inside the town on motorbikes, leaving their pickup trucks parked elsewhere. They appear to be melting into the population.

The head of France's military said it is plausible that the extremists would be willing to hide behind civilians. Guillaud said the militant groups have a history of taking human shields and France would do its utmost to make sure civilians are not wrongly targeted. "When in doubt, we will not fire," he said. He added that the French continued their airstrikes overnight on Tuesday to Wednesday. Targets destroyed so far include training camps, logistical depots, command centres and armoured vehicles that the jihadists had seized from Mali's government forces.

A French elite Special Operations soldier drives through the town of Markala, about 275 km from the capital Bamako. France will end its intervention in Mali only once stability has returned to the West African country, French President Francois Hollande said on Tuesday. (Francois Rihouay/Reuters)

French President Francois Hollande authorized the airstrikes last Friday after the Islamists began a push southward toward the capital from the northern half of Mali that they control. They seized the Afghanistan-sized north last April in the chaos following a coup in Mali's normally-stable capital, Bamako.

Sophie Langlois, Radio-Canada's Africa correspondent, reported from Bamako on Wednesday that 30,000 to 40,000 refugees from the north are in the city, and the numbers arriving have increased since the French offensive began.

Some households are hosting up to 20 refugees, she told CBC Radio's World Report.

However, the mood there is "much more joy and relief than worries."

The capital doesn't feel like it's part of a country at war, she said. "It's a feeling of a people happy that finally the world is looking at them and helping them to combat al-Qaeda."

Six days of airstrikes have done little to erode the Islamist gains in Mali, which some in the West fear could turn the region into a launching pad for extremist attacks. The bombardments began in the town of Konna, which the rebels occupied last Thursday. After initially saying they had stopped the rebel advance, France's defence minister on Tuesday acknowledged that Konna was still in the hands of the rebels.

The seizure of Diabaly brings the Islamists to only 400 kilometres from the capital. Konna, the closest point where they were known to be before, is 680 kilometres away.

On Tuesday, France announced it was tripling the number of troops deployed to Mali from 800 to 2,500. The offensive was to have been led by thousands of African troops pledged by Mali's neighbors, but they have yet to arrive, leaving France alone to lead the operation.

Canada sent one C-17 cargo plane to Mali on Tuesday to offer logistical support to the French, airlifting supplies to Bamako. It is expected to arrive in Mali Thursday.

With files from CBC News