French Interior Minister Nicolas Sarkozy has vowed to deport any Muslim cleric preaching violence.
Sarkozy said preaching incitement would not be tolerated
Speaking after meeting his Spanish counterpart in Madrid, Mr Sarkozy said he would seek the expulsion of imams in France "whose sermons are radical".
Mr Sarkozy said France and Spain had agreed tougher joint measures against Islamic militancy.
Two days ago, France reimposed border controls with its EU neighbours following the London bombings.
Call for unity
After meeting Spanish Interior Minister Jose Antonio Alonso, Mr Sarkozy told reporters radical preaching would no longer be tolerated in France.
"The [French] republic is not a weak regime and it does not have to accept speech which on the pretext that it is happening in a place of worship calls for hate and murder.
"Those who persist in this way will systematically be the object of an expulsion procedure."
Over the past decade France has expelled several foreign-born Muslim preachers after accusing them of abusing their positions by inciting violence.
The minister said Western countries must unite in the fight against al-Qaeda.
"I know of only one policy against these people - firmness, arresting them, punishing them, penalising them, in Madrid, London, New York, everywhere.
"We must never allow ourselves to give them the satisfaction of a division between us," he said.
Mr Sarkozy said he and Mr Alonso had agreed to strengthen co-operation in the fight against Islamic militancy.
France has stepped up security measures in the light of the London bombings, including restoring border controls with its EU neighbours.
On Thursday, French President Jacques Chirac warned that no country was immune from terrorist attacks.
"These terrorists have a mentality, a psychological state that is different from our own. All efforts must be made to fight against terrorism," he said.