PARIS: French troops started military operations on Friday against extremists in Mali, alongside forces from the West African country, dramatically upping the stakes in a conflict in a swath of lawless desert where al-Qaida-linked terrorism and kidnappings have flourished.    

France has led a diplomatic push for international action in northern Mali. But efforts to get an African-led force together, or to train the weak Malian army, have dragged.

The announcement came as the militants who control northern Mali advance ever closer toward the furthest town still under government control.

President Francois Hollande announced on Friday that in response to a request by Mali's president for help, ''French army forces supported Malian units this afternoon to fight against terrorist elements.''

''Mali is facing a terrorist aggression,'' Hollande said. He said the French operation would last ''as long as necessary'' and said it was aimed notably at protecting the 6,000 French citizens in Mali, a former French colony.

The move is risky for the four French hostages being held by extremists in Mali, who had threatened to retaliate if France intervened.

Hollande gave no operational details. Col. Abdrahmane Baby, a military operations adviser for the foreign affairs ministry, confirmed that French troops had arrived in the country but gave no details about how many were there or what they specifically were doing.

''They are here to assist the Malian army,'' he told reporters in the capital of Bamako.

The announcement comes after residents in central Mali said they had seen Western military personnel arriving in the area, and that planes had landed at a nearby airport throughout the night.

The arrival of the French also coincides with a major push south by the militants, who seized the town of Konna on Thursday.

It is the closest they have come to the town of Mopti, where the Malian military is located, since they grabbed control of northern Mali last year.