David Jackson

USA TODAY

President Obama reassured Baltic nations Wednesday that the United States and other NATO allies will defend them from the kind of Russian aggression on exhibit in nearby Ukraine.

"In this (NATO) alliance, there are no old members or new members, no junior partners or senior partners — there are just allies, pure and simple," Obama told an audience in Tallinn, Estonia.

He added, "We will defend the territorial integrity of every single ally."

Obama used the speech to denounce Russian aggression in eastern Ukraine, calling it a "brazen assault" on the territory of "a sovereign and independent European nation."

The incursion into Ukraine "challenges that most basic of principles of our international system," Obama said: "That borders cannot be redrawn at the barrel of a gun."

Ukraine is not a NATO member, and the U.S. and European allies are not obligated to defend it.

Three nations that border the Baltic Sea — Latvia and Lithuania as well as Estonia — have expressed concern about Russian aggression, and they have been NATO members for a decade.

Obama stressed the common defense requirements of the NATO alliance in a speech he delivered after meeting with the leaders of all three Baltic states.

Referring to the capital cities of the Baltic nations, Obama said that "the defense of Tallinn and Riga and Vilnius is just as important as the defense of Berlin and Paris and London."

Obama spoke shortly after a proposed cease-fire between Ukraine, Russia and pro-Russian separatists fell apart.

The speech capped a brief presidential visit to Estonia en route to a NATO summit in Wales, where Russia's incursion into Ukraine — and its impact throughout Eastern Europe — will be major topics.

NATO allies also plan to discuss the threat of the Islamic State in Iraq and Syria. The United States is conducting air strikes against IS in Iraq and considering possible action in Syria.

During his speech in Tallinn, Obama combined criticism of Russian President Vladimir Putin along with praise for how the Baltic nations broke away from the communist rule of the Soviet Union a quarter-century ago.

Democratic gains throughout Eastern Europe are threatened by Russia's aggression in Ukraine, Obama said, and the world must confront.

At one point, Obama said: "We'll be here for Estonia. We will be here for Latvia. We will be here for Lithuania. You lost your independence once before. With NATO, you will never lose it again."

As for Putin, Obama said the Russian leaders has repeatedly rejected a diplomatic solution in Ukraine. He said Putin is abetting violent separatists in eastern Ukraine, and he mocked Russian claims that its military forces are in the country on a humanitarian mission.

"They are Russian combat forces with Russian weapons in Russian tanks," the U.S. president said.

Obama said the U.S. and its allies are prepared to ratchet up economic sanctions on Russia and claimed that existing penalties are undermining the Russian economy.

"Russia's actions in Ukraine are weakening Russia," Obama said. "Russia's actions in Ukraine are hurting the Russian people."