NATO will discuss a possible larger Black Sea presence in October amid worries over a more assertive Russia, the alliance's Secretary General Jens Stoltenberg said on Friday.

Addressing reporters on day one of a two-day NATO summit in Warsaw, Stoltenberg said that several member states raised the need for an enhanced military presence in the Black Sea region.

"We decided to ask our military planners to provide advice for our defense ministers in October, to look into whether we can or how we can increase our presence not only on land… but also in the air and at sea," he said.

"We will be more concrete about that at our defense ministerial meeting in October," he added.

NATO leaders agreed on Friday to station multinational troops in four member states-Poland, Estonia, Latvia, and Lithuania-as a reassurance measure.