Spain says the men were trained by Bin Laden
The men, who are of Algerian origin, were arrested in cities across Spain overnight and in the early hours of Wednesday morning.
The operation, which the Spanish Interior Ministry says has dismantled one of Bin Laden's cells, was co-ordinated with other European police forces and is reported to be continuing.
In France, seven people have been place under formal investigation for an alleged plot to attack US interests there.
Forgery
The men are suspected of producing false documentation and forged credit cards for other activists based in Europe.
Public radio said that police believed they had channelled cash back to Algeria.
The Spanish Interior Minister Mariano Rajoy said their ultimate aim may have been to carry out suicide attacks similar to those on New York and Washington on 11 September.
Mohammed Atta, one of the suspected hijackers, who was part of a cell based in the north German city of Hamburg is known to have travelled extensively in Spain in July.
There is speculation he may have been meeting others in the Bin Laden network.
Mr Rajoy said the six men detained had been financed and trained by Bin Laden.
French plot
In France seven people have been put under formal investigation - a step towards being charged - in connection with an alleged plot to target US interests.
They have also been ordered into preventive detention, according to the French news agency, AFP.
French media reports say evidence found during their arrests in a dawn raid on Friday indicated they had been selecting locations for attacks on US assets.
The seven suspects are also believed to belong to the Bin Laden network.