“Should you even think of attacking one ally, you will be facing the whole alliance,” he declared at the close of the two-day NATO summit in southern Wales.

The NATO secretary general, Anders Fogh Rasmussen, said that the force, a “spearhead” for a larger reaction force, would send a clear message to potential aggressors, namely Russia, and would represent “a continuous presence.”

NEWPORT, Wales — NATO leaders approved plans Friday for a 4,000-person rapid reaction force to be based in Eastern Europe and meant to reassure members of the alliance unnerved by events in Ukraine, where Russia seized and annexed the Crimean peninsula and has backed separatist rebels in the east of the country.


In a press conference after the summit, President Obama said that the principle of collective defense was “nonnegotiable” and that NATO “will defend every ally.”

Obama said the leaders had agreed to a “new readiness action plan,” including the creation of the new force, the stationing of more equipment in Central and Eastern Europe, more rotations of forces into the area, and more training exercises there. He said all 28 allies would contribute to the effort “as long as necessary” and said members who were not already meeting the alliance’s goal of spending 2 percent of gross domestic product on defense would increase their military budgets.

“NATO will not be complacent,” Obama said.

Though Ukraine is not a member of the alliance, the president said, NATO was committed to upholding the country’s “sovereignty, independence, territorial integrity, and right to defend itself.” He said that all 28 allies would provide security assistance to Ukraine, including help with logistics and with command and control, and said NATO’s resolve would send “a strong message to Russia.”

Obama said the door to NATO membership “remains open to nations that can meet our high standards” and said the alliance will reinforce its cooperation with other countries as well. He specifically mentioned two, Georgia and Moldova, where Russian-backed separatist rebels have broken off chunks of territory from government control, as well as Jordan and Libya.


Earlier Friday, the Obama administration said it had formed a coalition of countries to oppose Sunni militants with the Islamic State group, unveiling a military and political campaign that officials said could eventually serve as a model for fighting extremist groups around the world.

But Ukraine remained the most important issue for the alliance, even as a cease-fire was announced Friday in Minsk, Belarus, by representatives of Ukraine, the pro-Russian rebels, Russia, and the Organization for Security and Cooperation in Europe.

The United States and the European Union have expressed skepticism about a cease-fire in the Ukraine conflict and said they were preparing further coordinated economic sanctions against Russia. Asked at the press conference whether those sanctions would go ahead if the cease-fire took hold, Obama gave a guarded answer. Though “the only reason we are seeing a cease-fire is the sanctions” against Russia, he said, European leaders were still discussing how and when to proceed with a new round.

“The path for Russia to rejoin the community of nations that respects international law is still there,” Obama said.

Britain said it will supply 1,000 troops, including a brigade headquarters, for the new NATO rapid reaction force, and that 3,500 British troops will take part in NATO exercises in Eastern Europe through 2015 — though there might be some overlap between the two commitments.


NATO also announced that its next summit, in 2016, will be held in Warsaw, the Polish capital, where “the Warsaw Pact was created and overthrown,” President Bronislaw Komorowski of Poland said.

Speaking from Minsk, negotiators said that the cease-fire would come into force at 11 a.m. Eastern Daylight Time.