Olga Rudenko

Special for USA TODAY

KIEV, Ukraine – President Obama said Tuesday that the world is prepared to strengthen sanctions against Russia, which he described as a "regional power" making trouble with its neighbors.

Speaking at the Hague, Netherlands, where he is attending a summit on international security, Obama said the West will not recognize Russia's illegal attempt to annex Crimea.

He insisted that Russia's military takeover of the Ukrainian province could be reversed.

"It is not a done deal," Obama said at a news conference.

Obama said there would be no military action by the West to dislodge Russia's troops, but more sanctions could be imposed beside those in place that target individuals in the inner circle of Russian President Vladimir Putin.

"We're not recognizing what is happening in Crimea," Obama said. He rejected "the notion that a referendum sloppily organized over the course of two weeks" would "somehow be a valid process."

Asked whether he agreed with Mitt Romney's assessment that Russia is the United States' top geopolitical foe, Obama said he is more concerned about a nuclear bomb in Manhattan than he is about Russia.

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

Romney, a Republican, lost to Obama in the 2012 presidential election.

Ukrainians who are waiting to hear from their leaders say they expected more from the United States and Europe.

"When the Crimea crisis started, some of the people I know were saying the West will allow this to happen as Ukraine was not important enough to quarrel with Russia over it," said Ivan Kovalchuk of Kiev.

"I didn't believe it, but it seems like truth after all. Putin just bit off a piece of our territory, and no one cared to stop him."

Dutch Prime Minister Mark Rutte, speaking with Obama, said Western nations had yet to agree on tougher sanctions to get Russia to end its annexation of Crimea.

"The Russia economy is very much gas- and oil-dependent. If economic sanctions will be necessary, and we are not there yet, these things will hit Russia very badly," he said.

The Senate advanced a bill Tuesday that would include $150 million in direct economic assistance and up to $1 billion in loan guarantees for Ukraine, and it would authorize sanctions on Russia.

In Ukraine, the Ukrainian parliament accepted the resignation of its defense minister as thousands of troops began withdrawing from the Crimean Peninsula. Igor Tenyukh said he rejected criticism that he had failed to issue clear instructions to troops on how to handle the infiltration of Russian troops and the takeover of Crimean offices by pro-Moscow militiamen.

The talks in the Netherlands were supposed to focus on nuclear security but have been overshadowed by the situation in Ukraine. Sides talks about Crimea are taking place between the United States and leaders of the world's top economies, known as the G-7.

Sanctions, including travel and asset bans, have been imposed on at least 33 Russian and Crimean individuals by the European Union and the United States after pro-Russian forces moved into the peninsula and annexed the region in an official ceremony last week.

Putin had been slated to take part in the G-7 talks when they began Monday, but the members — the United States, Britain, Canada, France, Germany, Italy and Japan — excluded Russia over the Crimea takeover.

In 1988, Russia was invited to join the informal group, which began to be referred to as the G-8.

Ukraine is pleading with the West to take steps to prevent further incursions into its country by the Russians.

In eastern Ukraine, there are people who support closer ties to Russia and others who want to pursue alignment with Europe.

One faction causing concern among Russia's allies is the Right Sector, a militarist organization that took part in street protests that ended with the ousting in February of pro-Moscow President Viktor Yanukovych.

The group is portrayed as aggressive fascists by the Russian state-controlled media that broadcast to eastern Ukraine, warning about the presidential candidacy of Right Sector leader Dmytro Yarosh in elections in May.

Alina Miroshnichenko, a supporter of the protests in Kiev, says the Right Sector does not represent all of the people of Kiev.

"Many are concerned about radical organization members carrying guns," she said. "I don't feel endangered by them, but I know that some people do. I hope that they find the place where they can serve the new Ukraine as fast as possible.

"They played a role in (protests), but so did thousands of other people."

Contributing: Susan Davis in Washington