Foreign affairs minister Stef Blok has called for a ceasefire in the Syrian civil war to be negotiated as soon as possible – but dismissed calls for further sanctions to be imposed on Russia.

Blok said a negotiated settlement in Syria brokered by the UN Security Council was needed to end the conflict. ‘The only way out of this is through negotiations,’ he said.

Russia has been criticised for vetoing an inquiry into alleged chemical weapons attacks in Douma and obstructing the work of the Hague-based Organisation for the Prevention of Chemical Weapons (OPCW), but Blok said sanctioning Moscow would be counterproductive. He backed the position of his German counterpart Heiko Maas, who said ‘without Russia there is no solution’.

OPCW officials said on Monday morning that inspectors had been unable to get into Douma, where president Bashar al-Assad’s forces are suspected of having killed at least 70 people with chlorine gas and sarin nerve agents a week ago.

The US, Britain and France launched a series of air strikes against Syrian government targets in the early hours of Saturday in retaliation for the alleged gas attack. The Dutch government said it understood the motive for the raids but did not support them because they were not backed by a security council resolution, Blok said.