The Nato military alliance has agreed on a new "spearhead" force amid growing concern at the Ukraine crisis and the rise of Islamic State militants.
The move was announced at a meeting of Nato leaders in Wales.
Talks on a ceasefire in eastern Ukraine have begun, but more clashes were reported close to the city of Mariupol.
Ukraine, Russia and pro-Russia rebels are attending the talks in Belarus, while Western countries ponder further sanctions on Russia.
The West accuses Russia of sending arms and troops to back the rebels in eastern Ukraine. Moscow denies this.
More than 2,600 people have died during the five-month conflict.
The enhanced sanctions are expected to target Russian banking, energy and defence, as well as what British sources call "Putin cronies".
But the UK says the sanctions will probably go ahead whether or not a ceasefire is agreed at the talks in the Belarus capital, Minsk.
"There is a great degree of scepticism about whether this action will materialise, whether the ceasefire will be real," UK Foreign Secretary Philip Hammond said.
"We can always take the sanctions off afterwards. I don't think we want to be distracted from our determination to impose further sanctions in response to Russia's major military adventure into Ukraine by these noises off about a possible ceasefire."
Ukrainian President Petro Poroshenko told the BBC he was "absolutely not confident" that peace could be achieved at the Minsk talks but "Ukraine as a state and me as Ukrainian leader are doing everything possible to have peace."
A continuation of the conflict would lead to "humanitarian catastrophe", he said.
On Wednesday, Russia's President Vladimir Putin announced a seven-point plan, including a halt to "active offensive operations" by the Ukrainian military and pro-Russia rebels, international ceasefire monitoring, unconditional prisoner exchanges and humanitarian aid corridors.
At the Nato summit, Secretary-General Anders Fogh Rasmussen said the new force - part of Nato's Readiness Action Plan - would number several thousand and would be able to deploy anywhere in the world in a matter of days.
"In these turbulent times, Nato must be prepared to undertake the full range of missions and protect allies against the full range of threats," he said.
"Should you even think of attacking one ally you will be facing the whole alliance."
Nato member countries bordering Russia have watched Russia's involvement in Ukraine with growing concern.
The UK has offered to contribute 1,000 personnel to the new force, which will have naval, air and special forces capability.
As the peace talks in Minsk got under way, fighting in eastern Ukraine continued.
Ukrainian government forces and volunteers are trying to hold on to Mariupol on the Azov Sea. The BBC's Fergal Keane, in Mariupol, tweeted that pro-Russia forces seemed to be hitting Ukrainian positions some 4km (2.5 miles) outside the city.
Large plumes of smoke could be seen as Ukrainian artillery fired back, he says. Ukrainian fighter jets also hit rebel positions.
War in eastern Ukraine: The human cost
- At least 2,600 people killed since mid-April (not including 298 passengers and crew of Malaysian Airlines MH17, shot down in the area)
- 951 civilians killed in Donetsk region alone, official regional authorities said on 20 August
- In some particularly dangerous places, such as Luhansk region, victims are said to have been buried informally, making accurate counts difficult
- Rebels (and some military sources) accuse the government of concealing true numbers
- 260,000 people have fled elsewhere in Ukraine while at least 814,000 have gone to Russia.
Ukrainian government forces have recently suffered losses of territory in both the Luhansk and Donetsk regions, and further south around Mariupol, which lies between Russia and Crimea - annexed in March by Russia.
Gunfire and shelling was also heard on Friday in Donetsk, the rebels' main base.
Volunteers with Ukraine's "Azov" battalion said they had begun a counter-offensive towards the rebel-held town of Novoazovsk, though this could not be independently confirmed.
Analysis: Jonathan Marcus, BBC defence and diplomatic correspondent
Nato's new Readiness Action Plan is the practical military response to the growing threats from around Nato's borders; not just from a resurgent Russia but also from the growing tide of instability in the Middle East.
It is all about being able to get more capable forces to areas of threat faster than ever before.
Existing rapid reaction forces will be re-vamped. A multi-national "spearhead" force with air, sea and land elements is to be established, capable of reinforcing a Nato ally within 48 hours.
This will require some headquarters, logistics and other elements to be established in eastern Europe and some supplies will need to be pre-positioned.
These reinforcement plans will also be extensively rehearsed through a stepped up pattern of exercises.
Intelligence gathering and analysis will be stepped up to give Nato planners a greater awareness of what is going on around the alliance's borders.
Nato leaders also discussed the growing threat of Islamic State (IS) in Iraq and Syria.
An IS video released on Tuesday showed the killing of US journalist Steven Sotloff, just days after the group beheaded another American reporter, James Foley.
In the latest video, an IS militant is seen threatening to kill a UK hostage, aid worker David Haines, who was seized in March 2013 in Syria's Idlib province.
Mr Rasmussen said Nato had pledged "seriously" to examine any plea by Iraq to fight IS militants.
The UK is deciding whether to arm the Kurds.