THE HAGUE (Reuters) - The Netherlands, joining other U.S. allies, voiced disquiet on Friday at the U.S. decision to withdraw forces from Syria and said Washington’s plan to reduce its military presence in Afghanistan was premature.

Thursday’s announcement by U.S. President Donald Trump surprised the Dutch, who contribute to military missions in Syria and Afghanistan, Defence Minister Ank Bijleveld told reporters in The Hague.

“It is clear to us that if you have an alliance you should discuss things within the alliance and not do things by tweet,” Bijleveld said.

The Netherlands supports the fight against Islamic State militants with F-16 war planes. The Dutch are set to end their participation in that operation, which falls under U.S. military command, on Dec. 31.

Bijleveld said an end to the U.S. military presence in Syria would have “far-reaching consequences for the region and security”. Islamic State has “not yet been completely defeated and the threat is not gone”, she said, a position at odds with Trump’s assessment.

The Dutch were also surprised by the announcement of Washington’s plans to significantly reduce its forces in Afghanistan, she said.

Bijleveld said it would be premature to scale back forces in Afghanistan, where the Netherlands has 100 troops in a NATO-led mission - known as Resolute Support - supporting Afghan army and police forces.

“We are intensifying efforts in Afghanistan because the security situation is not improving quickly enough,” she said.

She said the Netherlands was attempting to figure out what actual U.S. plans in Afghanistan are, as a major withdrawal was likely to make the mission unfeasible.