Any intervention in Syria under current circumstances is prohibited under international law without a mandate from the UN Security Council, Dutch government adviser Andre Nollkaemper said on Thursday.

The University of Amsterdam professor was requested for advice by the Dutch cabinet given the humanitarian emergency situation in Syria.

The United States, France and Britain have claimed there was enough proof of a chemical strike last week near Damascus by President Bashar Assad's regime. A team of UN researchers is currently investigating the possible use of chemical weapons.

"The breach of a customary prohibition on the use of chemical weapons by Syria, although it is very serious, provides no legal basis for the use of force," Nollkaemper said in a letter revealed by Dutch Minister of Foreign Affairs Frans Timmermans.

In addition, Nollkaemper doubted all conditions will be met for a humanitarian intervention."The important conditions for humanitarian intervention are the presence of an urgent need and that the primary purpose of the intervention should be to stop the violations. It should have the sole purpose to eliminate the threat to human lives,"he stated.

"An attack which is only classified as a punitive response does not fit in and does not support the right of humanitarian intervention. Such an attack can only be regarded as unlawful,"he said.