ITV News has been given special access to Nato exercises in Estonia, where only yesterday a Russian jet was found in international airspace.
NATO troops from around the world marked an Arctic military exercise by taking dozens of selfies.
Nato announces Awacs flights over Poland and Romania to monitor the crisis in Ukraine, as 200 troops take over a naval base in Crimea.
Nato has released satellite images that it says show Russian combat troops and "sophisticated heavy weaponry" inside Ukraine.
The images were taken in late August and reportedly show "self-propelled artillery" moving in convoy and establishing firing positions near the city of Krasnodon in eastern Ukraine.
In a statement, Nato said the images provide "concrete examples of Russian activity inside Ukraine" but represent "only the tip of the iceberg in terms of the overall scope of Russian troop and weapons movements".
Nato also said other images show Russian forces transferring weapons and other military hardware to separatist forces, and "substantial activity" on the Russian side of the border with Ukraine.
NATO Secretary General Anders Fogh Rasmussen has spoken of an alarming build-up of Russian ground and air forces close to the border with Ukraine.
He condemned Russia for sending a "so-called humanitarian convoy" into Ukraine without the consent of the Ukrainian authorities.
An independent Scotland would have to apply to join Nato as a new state, the head of the defence alliance has said.
Secretary General Anders Fogh Rasmussen said any decision to accept a new country would require the unanimous agreement of all 28 member states.
"In [the] case that Scotland voted in favour of independence then Scotland would have to apply for membership of Nato as a new independent state," he told The Times (£).
"Some aspiring countries have waited for many years. Others enjoy a very short procedure depending on how close they are to fulfilling the necessary criteria," Mr Rasmussen added.
Nato Secretary-General Anders Fogh Rasmussen said the alliance had seen what he called "a Russian incursion into Ukraine."
Responding to reports that a Russian column had entered Ukraine overnight, the Nato chief said: "It just confirms the fact that we see a continuous flow of weapons and fighters from Russia into eastern Ukraine and it is a clear demonstration of continued Russian involvement in the destabilisation of eastern Ukraine."
Mr Rasmussen also said Europe is becoming more dangerous and less stable.
Ukrainian forces made gains against pro-Russian rebels in east of the country, seizing the towns of Krasnogorovka and Staromikhailovka just outside of Donetsk.
The seizure brought the army to the edge of one of the last cities still in rebel hands following its advances in the past month. The other is Luhansk, near the border with Russia.
Shelling near the area where a Malaysian airliner was downed last month forced international experts to stop their search for victims at one part of the crash site, but a local ceasefire enabled them to work unhindered at the main part.
David Cameron has said Nato and its members "will not be intimidated" by Russia in the wake of its actions in Ukraine.
Speaking ahead of the Nato summit in south Wales next month the prime minister said the gathering marked a "pivotal" moment in Nato's history.
He said: "In 2014, the world is more unpredictable than ever. To the East, Russia has ripped up the rulebook with its illegal annexation of Crimea and aggressive destabilisation of Ukraine.
"To the South, an arc of instability spreads from North Africa and the Sahel, to Syria, Iraq and the wider Middle East.
"So we must use the Summit to agree how Nato should adapt to respond to and deter such threats; and to ensure the continued collective defence of all its members."
The summit near Newport is the first in the UK since Margaret Thatcher hosted the alliance in 1990, as the Cold War was ending and Nato started to chart a course for a new relationship with Russia.
Prime Minister David Cameron has said Nato must rethink its long-term relationship with Russia in the wake of its "illegal" actions in Ukraine.
He also called for Nato's members to take measures to ensure it can respond quickly to any threat from Moscow.
In a letter to his Nato counterparts, Mr Cameron said the measures should include sustaining a "robust" defensive presence in eastern Europe, keeping equipment and supplies in key locations and beefing up Nato's Response Force of swiftly deployable land, air, maritime and special operations troops.
The letter comes just days after a government report warned the trans-Atlantic military alliance was not adequately prepared for a potential threat from Russia.
Nato has promised to study a parliamentary report which said that Russia's destabilisation of the Ukraine had exposed "serious deficiencies" in its preparedness to deal with a military threat from its former Cold War adversary.
Oana Lugescu, a spokesperson for the alliance said: “This is an important report and we will study it carefully."
She added that the 28 member states had already taken steps to reinforce collective defense with more planes in the air, more ships at sea, and more exercises on the ground, especially in eastern Europe.
At the Wales Summit in September, she said Nato leaders will adopt an action plan to reinforce the readiness of the alliance to ensure it is able to deal with all the threats it faces.
She added: "We are also considering reinforcement measures, the designation of bases and pre-positioning of equipment and supplies. We are reviewing our defence plans, threat assessments, intelligence-sharing arrangements and early-warning procedures."
Sanctions curbing arms sales to Russia and cutting off financing to some of the countries banks were formally adopted by the European Union today.
Officials said the sanctions aim to inflict maximum pain on Russia and minimum pain on the 28 member states of the EU, but Russia denounced the sanctions as "destructive and short sighted."
Defence Secretary Michael Fallon said that Nato was taking the threat posed by Russia seriously.
"What's happened in the Ukraine is very much a wake-up call which the Nato leaders will be discussing at their summit in a month's time here in the UK," he said.
Mr Fallon said that Britain was contributing Typhoon fighter jets to the Baltic policing mission along with other Nato members.
An RAF surveillance aircraft was also in the sky over Ukraine's eastern border with Russia, he added.