The US military says its controversial Thaad missile defence system is "operational" in South Korea.

A spokesman said the system was now able to intercept North Korean missiles and defend the South.

But officials have told reporters that full operational capability is still some months away.

Tensions have been rising around the Korean peninsula, with repeated threats from North Korea and the presence of a group of US warships and a submarine.

On Monday, two US bombers took part in a joint drill with South Korea's air force in what the US said was a routine operation.

1. The enemy launches a missile

2. The Thaad radar system detects the launch, which is relayed to command and control

3. Thaad command and control instructs the launch of an interceptor missile

4. The interceptor missile is fired at the enemy projectile

5. The enemy projectile is destroyed in the terminal phase of flight

The launcher trucks can hold up to eight interceptor missiles.