NATO Secretary-General Jens Stoltenberg says an upcoming summit in Warsaw comes at a "critical time" as the alliance deals with Russian assertiveness and the threat of terrorism amid other challenges.

Stoltenberg was speaking Tuesday following talks with Poland's Defense Minister Antoni Macierewicz, who said that a bigger NATO presence in Eastern Europe would mean a greater sense of security for Poland.

The July 8-9 summit is to decide how many additional NATO troops to deploy in the east and where.

Stoltenberg said the summit comes amid a "more assertive Russia, intimidating its neighbors," violence in North Africa and the Middle east and terrorism, cyberattacks and ballistic missile proliferation.

He said NATO is responding by "implementing the biggest reinforcement of our collective defense since the end of the Cold War."