"The IS has been pushed back, but the threat is not over. There is a danger that the consequences of (Trump's) decision could hurt the fight against the IS and endanger what has been achieved," said German Foreign Minister Heiko Maas in a statement.

The battle against the Islamist militants would be "decided in the long run -- militarily and with civilian means", said Maas.

The foreign minister stressed the need for a political process under the auspices of the United Nations, in order to bring lasting stability back to war-torn Syria.