Live updates: follow the latest news on Russia-Ukraine
Nato, or the North Atlantic Treaty Organisation, was founded at the start of the Cold War to deter the Soviet Union from expanding and to prevent the rise of nationalist militarism in Europe.
Twelve founding nations launched Nato in 1949 and its ranks have now swelled to 30 countries (28 from Europe and two from North America). Three former Soviet republics — Latvia, Lithuania and Estonia — are members.
Is Ukraine in Nato?
Ukraine, itself a former Soviet republic, is not a member of the alliance.
In 2008, Nato promised that Ukraine, as well as Georgia, could join Nato. The alliance, however, did not specify a time frame.
The pledge infuriated Russian President Vladimir Putin, who claimed it betrayed a Nato promise not to expand eastward. The purported Nato assurance is disputed.
Ukraine is instead a partner of Nato.
As an alliance partner, Ukraine contributes to promoting democratic norms and supporting Nato-led missions. The organisation's programmes also help partner countries build their own defensive and security forces.
Ukrainian President Volodymyr Zelenskyy in 2020 approved his country's new National Security Strategy “with the aim of membership in Nato”, the alliance said.
And while Ukraine established relations with Nato in 1992 and has contributed to missions in Afghanistan and Iraq, it does not benefit from the organisation's collective defence commitment.
Under Article Five of the Nato agreement, an attack on one member of the alliance is considered an attack on all members.
This principle binds the 30 member countries to the concept of mutual protection, which is a cornerstone of the alliance. The only time it has been invoked was by the US in 2001, following the September 11 attacks.
US President Joe Biden reaffirmed America's commitment to Nato after Russia launched its invasion into Ukraine. His predecessor, Donald Trump, repeatedly bashed the alliance, accusing other members of not contributing enough towards defence.
“As I made crystal clear, the United States will defend every inch of Nato territory with the full force of American power,” Mr Biden previously said.
The US and its allies have supported Ukraine by supplying it with military equipment and have responded to the Russian invasion by issuing scores of sanctions.
However, because Ukraine is not a member, Nato has no remit to directly intervene in the conflict with Russia.
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A Ukrainian soldier walks past the shell of a burnt military vehicle, on a street in Kiev. AP -
A screengrab from CCTV footage shows a missile hitting a residential building in Kiev. Reuters -
A man inspects a broken window, after shelling carried out by Russian troops in the Ukrainian capital. Reuters -
Ukrainian soldiers take positions outside a military centre as two cars burn on a street in Kiev. AP -
Medical specialists transport a woman, who was wounded in the shelling of an apartment building, to an ambulance, as her husband looks on. Reuters -
A woman outside her apartment building after it was damaged by a rocket, in Kiev. AP -
A Ukrainian police officer detains a driver on a street in Kiev. AP -
A soldier's helmet with a bullet hole on a street in the Ukrainian capital. AP -
Ukrainian soldiers walk by a damaged vehicle, at the site of fighting with Russian troops, in Kiev. Reuters -
Ukrainian policemen move parrots to safety after a high-rise apartment block was damaged by shelling in Kiev. EPA -
A screengrab from a video shows rescue workers carrying a person at the site of a damaged multi-storey residential building, south-west of the Ukrainian capital. Reuters -
A building damaged by shelling carried out by Russian troops in Kiev. EPA -
Helga Tarasova comforts her daughter Kira Shapovalova as they wait in an underground shelter during a bombing alert in Kiev. AFP -
A man walks past a building damaged by a rocket attack in the Ukrainian capital. AP -
Emergency services workers near an apartment building damaged by shelling in Kiev. Reuters -
Ukrainian soldiers collect unexploded shells in the capital. AFP -
An apartment building damaged by shelling in Kiev. Reuters -
Debris of a burnt military truck on a street in Kiev. AP -
Natali Sevriukova stands next to her home after a rocket attack in Kiev, Ukraine. AP -
People on foot and in cars move to cross from Ukraine to Poland at the Korczowa-Krakovets border crossing following the Russian invasion of Ukraine. AFP -
Servicemen from the Ukrainian National Guard in central Kiev. Reuters -
Ukrainian soldiers in downtown Kiev after Russian troops reached the outskirts of the capital. AP Photo -
Police officers detain demonstrators in St. Petersburg, Russia. Hundreds of people gathered in Moscow and St. Petersburg on Thursday, protesting against Russia's attack on Ukraine. Similar protests took place in other Russian cities, and activists were also arrested. AP Photo -
Hungarian troops in Vasarosnameny, close to the border with Ukraine, prepare to help refugees. AP Photo -
Wrecked Russian army rocket launchers in Kharkiv, Ukraine. Reuters -
The aftermath of a rocket attack in Kiev. AP Photo -
A US Air Force jet refuels over Poland. Reuters -
Devastation after shelling in Ukraine's Luhansk enclave. Reuters -
The Royal Welsh Battlegroup from the UK makes its way to Estonia. Reuters -
Firefighters tackle a blaze in a building in Kiev. AFP -
The wreckage of an unidentified aircraft in a residential area in Kiev. Reuters -
Smoke rises near the Ukrainian Defence Ministry in Kiev. Reuters -
Russian military helicopters fly over the Ukrainian capital. AP -
An anxious wait to board a train to leave Kiev as the attack loomed. AP Photo -
Ukrainian servicemen on tanks in the Donetsk region, eastern Ukraine. AP Photo -
Ukraine troops said this destroyed armoured vehicle outside Kharkiv belonged to the Russian army. Reuters -
Rescuers at the crash site after a Ukraine armed forces Antonov aircraft was shot down in Kiev, according to the Ukrainian authorities. Reuters -
Ukrainian tanks that aim to repel an attack by the Russian military in the Luhansk enclave of Ukraine. AFP -
A Ukrainian State Border Guard Service base is ablaze after heavy shelling near Kiev. Reuters -
Damaged radar at a Ukrainian military plant outside Mariupol. Officials in Kiev say Russian troops have rolled into the country from the north, east and south. AP Photo -
Firefighters attend a blaze after bombing in the eastern Ukrainian town of Chuguiv, as Russian armed forces appeared to be bombarding Ukraine from several directions. AFP -
A traffic jam in Kiev, with many Ukrainians leaving their capital after Russian troops entered. EPA -
The Border Service of Ukraine released CCTV footage purporting to show Russian military vehicles passing a checkpoint to drive into Crimea. AP -
A man picks up fragments of military materiel on the street after an apparent Russian strike in Kharkiv, Ukraine. AP -
Workers load the debris of a rocket on to a lorry in the aftermath of Russian shelling in Kiev. AP -
Emergency staff treat an injured man after bombing in Chuguiv. AFP -
An American woman in distress after crossing the border to flee the violence in Ukraine, in Medyka, Poland. Reuters -
People take shelter in a Kiev subway station, after Russian President Vladimir Putin authorised a military operation in eastern Ukraine. Reuters -
People in a rush near Kiev-Pasazhyrskyi railway station in the Ukrainian capital. AFP -
A Flightradar24.com screengrab shows a dearth of civilian aircraft in Ukrainian airspace after the Russian invasion. AP -
The aftermath of bombing in Chuguiv. AFP -
A Ukrainian rocket launcher vehicle prepares for action. Reuters -
Cars are driven across a field to leave the city of Kharkiv. Reuters -
People chant, carry placards and wave Ukrainian flags as they gather in Sydney, to demonstrate against Russian attacks on its neighbour. AP -
People with many of their belongings packed take shelter in a Metro station in Kiev. AFP -
Emergency services at the scene of an explosion at a military unit building in Kiev. EPA -
A Kiev resident sweeps up debris after Russian shelling. AP -
The first 40 soldiers of the 173rd US Army Airborne Brigade step off a military plane in Latvia. EPA -
More damage from shelling in Kiev. AP -
People wait at a bus station to travel to western parts of Ukraine, after violence in the east. Reuters -
A woman carries her cats in a quest for a safe haven. AFP -
Ukrainian President Volodymyr Zelenskyy holds an urgent government meeting in Kiev to discuss the next step. AFP -
European Commission President Ursula von der Leyen and foreign policy chief Josep Borrell give a joint statement in Brussels, updating the press about the situation in Ukraine. EPA -
People survey the damage after bombing in Chuguiv. AFP -
A building on fire in Chuguiv. AFP
