THE HAGUE (Reuters) - U.S. President Barack Obama on Tuesday called Russia a “regional power” that had seized part of Ukraine out of weakness rather than strength, in a dig at President Vladimir Putin.

Putin has tried to rebuild Russia’s prestige since the collapse of the Soviet Union and project Moscow as a strong player on the international stage.

Obama, who has had a cool relationship with Putin since he regained the presidency, dismissed that role during a news conference after a nuclear summit in the Netherlands that has been overshadowed by Russia’s annexation of Crimea.

“Russia is a regional power that is threatening some of its immediate neighbors, not out of strength but out of weakness,” Obama said.

“We (the United States) have considerable influence on our neighbors. We generally don’t need to invade them in order to have a strong cooperative relationship with them,” he said.

Obama’s comment was an example of how far apart the leaders have grown over the past year in relations marked chiefly by differences in their approach to hot-button issues from Syria to Iran.

The Ukraine crisis has prompted a reassessment of the U.S. relationship with Russia, one not aimed at re-fighting the Cold War but rather using the strength of international alliances to isolate Russia and bolster NATO’s commitment to defend allies near Russian borders.

During the news conference, Obama shied away from assigning motives to Putin, avoiding the type of speculation that has seen some Republican lawmakers back home say they think Putin is trying to reassemble the Soviet Union.

And he avoided getting personal with Putin himself, after drawing headlines last year by saying the Russian president had “that kind of slouch, looking like the bored kid at the back of the classroom.”

In so doing, Obama also managed to dismiss a Republican critic, former Massachusetts Governor Mitt Romney, who went into something of a political exile for a year after Obama defeated him in the 2012 election and has resurfaced on Sunday U.S. news television shows to criticize Obama’s foreign policy.

Romney drew criticism from Obama during the 2012 campaign for declaring Russia a top U.S. geopolitical foe.

On Tuesday, Obama said Russia was not the number one U.S. national security threat and said he was more concerned about the possibility of a nuclear weapon going off in Manhattan.