BAMAKO, Mali – French soldiers pressed north in Mali territory occupied by radical Islamists on Wednesday, launching a land assault that was to put them in direct combat with al-Qaida-linked fighters “in one to 72 hours,” military officials said.

Their presumed destination was the town of Diabaly, where fleeing residents said Islamist extremists had taken over their homes and were preventing other people from leaving. They said the militants were melting into the population and moving only in small groups on streets in the mud-walled neighborhoods to avoid being targeted by the French.

“They have beards. And they wear boubous (a flowing robe). No one approaches them. Everyone is afraid,” said Ibrahim Komnotogo, who was out of town when the militants seized Diabaly over the weekend but kept in contact by telephone with other residents.

In apparent retaliation for the French offensive, the same group controlling northern Mali occupied a natural gas complex in neighboring Algeria, taking dozens of people hostage, including Americans.

French ground operations in Mali began overnight, France’s military chief of staff said on Europe 1 television Wednesday. He stressed that French infantry units “will be fighting directly in the coming hours.”