The US says it has seized a North Korean cargo ship, accusing it of violating international sanctions.

The justice department said the ship was used to transport coal, North Korea's largest export but subject to a UN export ban.

The vessel was initially impounded in Indonesia in April 2018.

It is the first time the US has seized a North Korean ship for breaching sanctions and comes amid worsening relations between the two.

A meeting between North Korean leader Kim Jong-un and US President Donald Trump ended without agreement in February with the US insisting North Korea give up its nuclear programme and Pyongyang demanding sanctions relief.

North Korea has carried out two weapons tests in the space of the past week in what is widely seen as an attempt to increase pressure on the US over its failure to make concessions.

What do we know about the ship?

The vessel, the Wise Honest, was first seized last year and the US filed a seizure warrant in July 2018.

Indonesia has handed over the ship, and it is now on its way to the US.

US officials stressed that the announcement had nothing to do with the North Korean tests.

"Our office uncovered North Korea's scheme to export tons of high-grade coal to foreign buyers by concealing the origin of their ship, the Wise Honest," said US prosecutor Geoffrey S Berman.

"This scheme not only allowed North Korea to evade sanctions, but the Wise Honest was also used to import heavy machinery to North Korea, helping expand North Korea's capabilities and continuing the cycle of sanctions evasion."

Payments for the maintenance of the Wise Honest were allegedly made in US dollars through unsuspecting US banks - giving the US authorities the opportunity to mount an unusual civil forfeiture legal action.

North Korea has been the subject of a series of US and international sanctions over Pyongyang's development of nuclear weapons and missile tests.

Can the US and North Korea get back on track?

Most of the developments concerning the two countries point to a return to animosity but the US Special Representative on North Korea Stephen Biegun is currently in South Korea to discuss ways of restarting denuclearisation talks.

President Trump has said "nobody's happy" about the latest North Korean tests.

"I know they want to negotiate, they're talking about negotiating. But I don't think they are ready to negotiate," he said.

He became the first sitting US president to meet his North Korean counterpart when they met last year but despite this, and a follow-up meeting, there has been little tangible progress towards the stated goal of ridding the Korean peninsula of nuclear weapons.

Last year, Mr Kim said he would stop nuclear testing and would no longer launch intercontinental ballistic missiles but nuclear activity appears to be continuing.

One of the few concrete outcomes of their talks - joint efforts to retrieve the remains of US servicemen killed in the Korean war - has been halted.