What is Nato and which countries are members?

Donald Trump's suggestion that he would "encourage" Russia to attack Nato members failing to spend enough on defence has been condemned by the head of the military alliance.

The former US president's comments, about countries which do not meet Nato's target of spending 2% of national income on defence, put European and US troops at greater risk, Jens Stoltenberg said.

Nato, which brings together countries from Europe and North America, is recruiting new members and bolstering its defences following Russia's invasion of Ukraine.

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

Its aim was to block expansion by the then Soviet Union - a group of states which included Russia.

Members agree that if one of them is attacked, all other nations should help it - which could include using armed force.

Nato does not have an army of its own, but member countries can take collective military action in response to crises. They also coordinate military plans and carry out joint military exercises.

After Russia's invasion of Ukraine in February 2022, Nato said that it posed the "most significant and direct threat to allies' security".

Nato has 31 members across Europe and North America.

After the Soviet Union's collapse in 1991, many Eastern European countries joined: Albania, Bulgaria, Hungary, Poland, the Czech Republic, Slovakia, Romania, Lithuania, Latvia and Estonia.

Sweden and Finland applied to join in May 2022, following Russia's invasion of Ukraine. The two countries feared for their security.

Finland - which has a 1,340km (832 mile) land border with Russia - became a Nato member in April 2023.

Now, Sweden only needs Hungary's parliament to approve its membership.

Bosnia and Herzegovina, and Georgia, also want to join Nato.

Nato asks member states to spend at least 2% of their national income on defence.

The US spends nearly 3.5% and countries which border Russia - such as Poland and the Baltic Republics - spend more than 2% on their militaries.

The UK spends just over 2%.

However, countries such as France, Germany, Italy and Spain spent under the minimum level in 2023.

Nato has said that Ukraine can become a member, but has not confirmed when this will happen.

It refused Ukrainian President Zelensky's request for "fast-track" membership in September 2022.

Russia has consistently opposed the idea of Ukraine joining Nato, fearing it would bring the alliance's forces too close to its own territory.

Kyiv accepts it cannot join Nato while it is at war with Russia, but wants to join as soon as possible after fighting ends.

Since July 2023, the Nato-Ukraine Council has coordinated efforts to help Ukraine defend itself against Russia.

As a group, Nato has not sent weapons to Ukraine, but several individual member countries have done so.

The US, UK, Germany and Turkey have provided anti-tank weapons, missile defence systems, artillery guns, tanks and military drones.

The US and UK have also supplied long-range missiles.

The US has let Nato countries offer its fighter jets, such as F-16s, to Ukraine, and teach pilots how to fly them.

The Netherlands said it may soon deliver 18 F-16 jets.

However, Nato countries are not sending troops to Ukraine, or using their air forces to impose a no-fly zone over the region, because that could provoke a direct conflict with Russia.

In 2023, Nato commanders agreed detailed plans for countering possible Russian attacks in the Arctic and north Atlantic, central Europe, or the Mediterranean region.

In February 2024, Nato will stage one of its largest military exercises since the end of the Cold War.

The Steadfast Defender exercise in Eastern Europe will involve 90,000 personnel from all 31 Nato countries plus Sweden. The UK is sending 20,000 personnel.

Nato previously announced plans to increase the number of its troops in Europe on high alert from 40,000 to more than 300,000.

It has also bolstered its defences on its eastern flank, bordering Russia.

There are currently eight battlegroups in Bulgaria, Hungary, Romania, Slovakia and the Baltic Republics. Before the war in Ukraine, there were four.