Police in the north German city of Bremen have warned of a heightened danger from Islamist militants and said they had increased their presence in the city centre and stepped up protection of the Jewish community.

They said in a statement they had searched an Islamic culture centre, detained several people for identity checks and arrested one person in connection with the measures. A spokesman for the police declined to give further details.

"Since yesterday evening the authorities in Bremen have indications, based on knowledge from the police, the domestic intelligence agency and a federal authority, of an increased threat from Islamist extremists," the police statement said.

Earlier this month a carnival parade in the northern German town of Braunschweig was cancelled at short notice due to a threat of an Islamist attack.