US President Barack Obama will visit Estonia and attend a Nato summit in Wales next week to send a strong message to Russian President Vladimir Putin that his incursion into Ukraine must be reversed and to keep his hands off the Baltic nations.

A fresh move into eastern Ukraine by Russian forces in support of separatists is rattling the region, and Obama will reassure Nato's Baltic allies Estonia, Latvia and Lithuania that the alliance will stand with them should Moscow turn its attention to them.

It will be the second visit ever to Estonia by an American president, following George W. Bush's 2006 stop there. Obama will meet all three Baltic leaders together and give a speech on Wednesday.

The White House said Obama will stress that the alliance's Article 5 commitment to the common defense of each member is an ironclad guarantee.

"Russia, don't even think about messing around in Estonia or in any of the Baltic areas in the same way that you have been messing around in Ukraine," Charles Kupchan, the senior White House director for European affairs, said on Friday in laying out Obama's mission.

The Nato summit will put Obama in the same room with many European leaders who have joined with him in imposing economic sanctions on Moscow for its move into Ukraine and he has said Washington is considering stiffening those sanctions.

A focus of the summit will be to shift attention of the alliance toward the east as a bulwark against any Russian expansionism in Eastern Europe.

Ukraine has asked for Nato for membership, but there is no consensus within Nato for enlarging the alliance.

Also overshadowing Obama's trip will be how to confront a challenge from Islamic State militants who have a stronghold in Syria and have made gains against government forces in Iraq.

Nato diplomats said a leaders' dinner next Thursday will be dominated by talks on what they said is the increasingly prominent threat posed by Islamic State at Nato's southeastern corner along Turkey's border with Syria and Iraq.

One challenge for Obama on the trip will be to persuade Nato leaders to step up defense spending. European governments have lagged in their commitment to provide 2 percent of GDP to defense because of lingering economic woes.

Kupchan said he is reasonably optimistic of an agreement among the 28 Nato allies to rally behind a commitment toward increased spending.-Reuters