German police have raided the homes of seven people on suspicion they supported the jihadist group Islamic State (IS) fighting in Syria and Iraq.

Police say the suspects were planning a violent attack.

"We will not stand by and watch as the terrorist Islamic State death squads in Syria and Iraq get support from Germany," interior minister for the southern state of Bavaria, Joachim Herrmann, said.

The raids were based on information that an ambulance vehicle financed through fundraising events in Germany was taken to Syria and turned into an improvised military personnel carrier with a mounted semi-automatic gun.

Other off-road vehicles were also taken to the combat zone, where IS jihadists have swept across a large area of war-torn Syria and Iraq in recent months, authorities said.

No arrests were made, but evidence was seized including computers, hard drives and electronic data.

The raids targetted the homes of five suspects in Bavaria and others in Lower Saxony and North Rhine-Westphalia states.

A mosque and an Islamic centre were also raided.

Berlin this month formally outlawed active support for the IS group, including recruiting fighters and social media propaganda.

Security agencies estimate 400 German citizens have been, or are, fighting with the jihadists in Syria and Iraq.

Authorities are set to prosecute at least 30 suspected jihadists who have returned to Germany over their activities in Syria.

Last Friday, German Muslims at more than 2,000 mosques condemned the actions of IS in a nationwide day of prayer and vowed to stem the tide of youngsters heading to join radical militants in Syria and Iraq.

AFP/Reuters