NATO chief Jens Stoltenberg said Tuesday he expected a decision "soon" on sending German-made Leopard tanks to Ukraine, as pressure grows on Berlin to give the go-ahead.

"We must provide heavier and more advanced systems to Ukraine, and we must do it faster," Stoltenberg said during a visit to Berlin.

"We discussed the issue of battle tanks. Consultations among our allies will continue and I'm confident that we will have a solution soon."