TALLINN - US President Barack Obama reaffirmed on Wednesday NATO'S steady alliance with Baltic states saying that the US would unconditionally come to the defense of its small Baltic allies in case of need.

He said in a written speach that the US would never condone or recognize "the Russian invasion and annexation of any part of Ukraine".

US President Barack Obama speaks during his remarks at the Nordea Concert Hall in Tallinn, Estonia, Sept 3, 2014. [Photo/Agencies]

Obama clarified the US and NATO's stance towards Estonia and the other two Baltic states Latvia and Lithuania in a keynote speech on Wednesday in Tallinn, the capital of Estonia where he paid a 12-hour-long visit.

"You lost your independence once, (but) with NATO you will never lose it again", he said.

"We have no interest in weakening Russia," Obama also said. "We do not seek out confrontation with Russia."

Obama said that the US had always supported the development of the rule of law in the country.

"That path remains available to Russia," said the president. "But it's a path that starts with Russia changing course and leaving Ukraine so Ukrainians can make their own decisions."

He also reserved a section of his address for Ukraine and the necessity of civil reforms, before calling on NATO to send an unmistakable message to Ukraine as well.

"Ukraine needs more than words," said Obama.

Obama's speech also largely dedicated to reassurance of newer allies, representing perhaps the most powerful expression of support from the US over the last 23 years of restored diplomatic relations.

Obama ended his 12-hour-long visit with joint remarks with Estonian Prime Minister Taavi Roivas to the American and Estonian military service members in Estonia.