Ukrainian President Volodymyr Zelensky has issued a stark warning that Russian leader Vladimir Putin could be prepared to strike NATO within the next five years. He urged the alliance to expedite plans to bolster defense spending.

The Ukrainian leader says that his country is holding Russia up for now, but that Putin could be ready to hit a NATO country within a matter of years.

The alliance’s summit will minimize references to either Russia or Ukraine to avoid antagonizing the U.S. president who has sided with the aggressor.