NATO Secretary-General Anders Fogh Rasmussen said leaders of the alliance have approved a "spearhead" force to address the threat of Russian aggression.
He said the spearhead, to be created within an existing rapid response force, could deploy several thousand land troops in the alliance's eastern members within "a few days."
Rasmussen, speaking at a NATO summit in Wales on September 5, also warned Moscow that no third country has a veto on NATO expansion -- a signal that Ukraine and other countries must not be barred from seeking membership if it chooses to do so.
The two-day summit was dominated by the conflict in eastern Ukraine, where Kyiv and NATO say Moscow has sent thousands of troops and hundreds of tanks and other military hardware to help pro-Russian separatists fight government forces.
Rasmussen said the rapid response force would allow NATO to "maintain a continuous presence...in eastern parts of the alliance on a rotational basis."
He said it would ensure a continued presence in the air, on land, and at sea.
The command and control center will be located near the northwestern Polish city of Szczecin, but Rasmussen said the three Baltic states and Romania have also indicated they are willing to host related facilities.
Rasmussen said there will be prepositioned equipment, supplies, and planners in the eastern members of NATO and that intelligence-sharing and defense plans will be upgraded.
He said there will also be joint exercises held on short notice.
The secretary-general added that such plans send a clear message that NATO protects all of its allies "at all times."
Rasmussen said NATO leaders also agreed to substantive measures to help Georgia -- whose NATO aspirations accelerated after its short war with Russia in 2008 -- advance toward membership.
The package includes the creation of a NATO mission in Georgia to modernize the defense sector, an expansion of the NATO liaison office there, military exercises in the country, as well as a possible training center.
Along with Georgia, Rasmussen said Montenegro had made progress in its efforts to join the alliance, reiterating that no third country has a veto over NATO enlargement.
He said NATO will open "intensified and focused talks" on Montenegro's candidacy and that an assessment on whether the western Balkan country could join NATO will be made by the end of 2014.
Meanwhile, British Prime Minister David Cameron said at the NATO summit that alliance leaders condemn the "barbaric and despicable acts" carried out by Islamic State militants and that threats by the extremist group will only harden the NATO leaders' resolve to stand up for their values.
U.S. Secretary of State John Kerry called for a plan to counter the militant organization to be prepared in time for the UN General Assembly later this month.
He urged 10 allies to contribute in some form towards countering the threat from Islamist militants.
A Western official at the summit said NATO would help coordinate security assistance for Iraq.
Islamic State fighters who have seized large parts of Syria and northern and western Iraq have been accused of executing hundreds of Iraqi soldiers and carrying out massive abuses against religious and ethnic minorities.
The militants recently beheaded two U.S. journalists and have threatened to kill a British hostage.
The NATO summit was wrapping up as representatives of Ukraine and the rebels met in Minsk for talks that could produce a cease-fire and agreement on steps to end the conflict that has killed more than 2,600 people since April and set Russia off against the West.
With reporting by Rikard Jozwiak in Brussels and AFP, Reuters, and AP.