Ukraine conflict: What is Nato and will Finland and Sweden join?

Version 25 of 31.

Boris Johnson has said the UK would support Sweden and Finland if they came under attack. Both countries are considering whether to join Nato, with a decision expected shortly.

The US has also said it would support them in the period between applying and then becoming members of the defence alliance.

Nato countries are currently supplying Ukraine with billions of dollars worth of weapons to counter Russia's invasion.

What is Nato?

Nato - the North Atlantic Treaty Organization - is a military alliance formed in 1949 by 12 countries, including the US, UK, Canada and France.

Members agree to come to one another's aid in the event of an armed attack against any individual member state.

Currently 30 countries are members of Nato

Nato's aim was originally to counter the threat of post-war Russian expansion in Europe.

Soviet Russia responded by creating its own military alliance of eastern European communist countries, called the Warsaw Pact.

After the Soviet Union's collapse in 1991, most former Warsaw Pact countries joined Nato.

Will Sweden and Finland join Nato?

Sweden and Finland are expected to announce their decisions within days.

Nato secretary general Jens Stoltenberg has said they would be welcomed if they did apply, and that the joining process would be quick.

Are Sweden and Finland going from neutral to Nato?

Is Nato's Nordic expansion a threat or boost to Europe?

Both countries have long pursued policies of military neutrality. Were they to join, it would take the Nato alliance to 32 members.

Finland shares a 1,340km (830 mile) border with Russia, which has warned both countries against joining, threatening a "military technical response".

However, US defence officials say that Moscow's invasion of Ukraine has been a "massive strategic blunder" that is likely to bring about Nato enlargement.

Why isn't Nato sending troops to Ukraine?

As Ukraine isn't a Nato member, the alliance isn't obliged to come to its defence.

Nato countries fear that if their troops confront Russian forces in Ukraine, it could lead to an all-out conflict between Russia and the West.

Nato says its members are "determined to do all we can to support Ukraine," but must ensure the war doesn't escalate beyond Ukraine's borders.

This is why Nato rejected imposing a no-fly zone over Ukraine.

However, it has approved setting up four new multi-national battlegroups in Slovakia, Hungary, Bulgaria and Romania - three of which border Ukraine - doubling Nato's presence in the region.

Why is Russia opposed to Nato?

Nato offered Ukraine a path towards membership in 2008. After Russia's annexation of Crimea in 2014, Ukraine made joining a priority.

But this has not happened, mainly because of Russia's long-standing opposition.

One of Russia's demands before the invasion was that Ukraine should never be allowed to join - something Nato refused to accept.

Russia believes Nato has been encroaching on its area of political influence by taking on new members from eastern Europe, and that admitting Ukraine would bring Nato right into its backyard.

Ukraine's President Zelensky has accepted his country can't join Nato at present, saying: "It is clear that Ukraine is not a member of Nato. We understand this."

China joins Russia in opposing Nato expansion

Which weapons have the UK and other countries sent to Ukraine?

Initially, Nato countries limited their supplies to defensive weapons.

The UK sent Ukraine thousands of NLAW anti-tank missiles and some Starstreak anti-aircraft missiles.

The US sent Javelin anti-tank missiles and Stinger anti-aircraft missiles.

Initially, western countries sent defensive weapons such as anti-tank missiles to Ukraine

Slovakia sent its S-300 anti-aircraft defence system, which can destroy aircraft up to 400km away. The US and Turkey have both sent drones armed with missiles.

But several Nato countries have now significantly stepped up their supplies and are sending heavier weapons - such as long-range artillery - to enable Ukraine to counter-attack Russia's army, and they are planning massively to increase the amounts they are spending on military aid.

The US is now sending helicopters, artillery and armoured personnel carriers.

US President Joe Biden is asking Congress to approve a $33bn (£26bn) grant for security and economic assistance to Ukraine on top of the $3.7bn (£3bn) it has already spent.

The UK is offering an extra £300m in military support to Ukraine and is planning to send armoured vehicles, electronic warfare equipment, anti-artillery radar systems and night vision devices.

France is among those countries now supplying Ukraine with long-range artillery

The Czech Republic has sent T-72 tanks and armoured infantry carriers

Australia is sending armoured vehicles

Canada is sending artillery

France and the Netherlands are sending self-propelled artillery

Germany is sending anti-aircraft tanks

The EU has said it will spend up to 450m euros (£376m) to fund the supply of weapons to Ukraine - the first time the EU has helped provide arms to a warzone.

Are arms shipments to Ukraine making a difference?

How many troops does Nato have in Eastern Europe?

Nato already had troops stretching from the Baltic in the north to Romania in the south.

They had been stationed there in 2014, after Russia's annexation of Crimea - designed to act as a "tripwire" in case of a Russian attack.

Nato has stepped up its military defences in eastern Europe

Nato has now sent elements of its 40,000-strong Response Force to countries bordering Russia and Ukraine.

It has fighter jets on alert and naval ships, including aircraft carrier groups, patrolling the seas.

The US is sending more troops to join Nato's existing four multinational battlegroups in Estonia, Latvia, Lithuania and Poland, and the multinational brigade in Romania.