NATO is set to considerably increase forces it has deployed on its eastern flank, Secretary-General Jens Stoltenberg said on Wednesday.

Addressing a news conference on the eve of an extraordinary NATO summit to discuss the ongoing Russia-Ukraine conflict, Stoltenberg said he expected allies to agree to strengthen NATO's position "on land, in the air and at sea."

"The first step is the deployment of four new NATO battlegroups in Bulgaria, Hungary, Romania and Slovakia. Along with our existing forces in the Baltic countries and Poland, this means that we will have eight multinational NATO battlegroups all along the eastern flank, from the Baltic to the Black Sea," he said.