With US approval, Denmark and the Netherlands announced in August they would provide up to 61 jets, once Ukrainian pilots had been trained up.

Approval is required for re-exports of military equipment, and the government said Friday the planes will require further testing before they can be delivered.

"Today I informed President (Volodymyr) Zelensky of our government's decision to prepare an initial 18 F-16 fighter aircraft for delivery to Ukraine," the Dutch defence minister said in a statement, without providing a delivery date.

Besides an export permit, a number of other criteria must also still be met before delivery can take place, including requirements for personnel and infrastructure, the statement said.

Outgoing Dutch Prime Minister Mark Rutte said "this decision confirms the Netherlands' undiminished commitment to providing Ukraine with the support it needs to respond to the ongoing Russian aggression."

Zelensky said that he spoke to Rutte and thanked him for the support.

"We discussed frontline developments, the situation in the Black Sea and Ukraine's current military needs," he added.

The Netherlands last month sent five F-16s to Romania, where they are being used to train Ukrainian pilots.