A rescue boat carrying dozens of refugees in the Mediterranean Sea has had its registration revoked by Panamanian authorities following pressure from Italy's right-wing government, two humanitarian groups claim.

SOS Mediterranee and Doctors Without Borders, two non-governmental organisations, jointly operate Aquarius 2 under Panama's flag near the region's notorious trafficking route, where 1,600 people have died trying to cross to Europe this year alone.

Both claimed in a statement that Panama had removed the ship's registration "under blatant economic and political pressure from the Italian government".

Panama's maritime authority said in a statement that it has begun procedures to remove Aquarius 2's registration, after Italy complained that the boat's captain failed to follow orders.

The organisation added that although the "principal complaint came from Italian authorities", officials in Gibraltar had also removed the boat's registration and had requested that Panama suspend its operations.

It also said Italy claims the captain defied instructions to return refugees rescued from unsafe vessels back to Libya.

The vessels were initially launched by Libyan traffickers, but the NGOs say that the North African country fails to meet international standards for safe harbour, in order for the rescued refugees to be returned.

Libya is currently gripped by extreme violence amid a surge of fighting between rival militias.

Refugees who are forced to return there are held in detention centres where sexual assault is common and food scarce.

Italy claims that returning rescued refugees to Libya will discourage human trafficking, but international maritime law says that those rescued at sea should be brought to the nearest safe harbour.

Despite this, private rescue boats are unable to dock in Italy, after being banned by Matteo Salvini, the country's anti-refugee deputy prime minister.

Mr Salvini denied that Italy was linked to the decision over the Aquarius 2 in a tweet posted on Sunday night, writing that there was "no pressure at all on Panama for the Aquarius 2. I don't even know Panama's area code".

Aquarius 2 was carrying 58 rescued refugees. As of Sunday night it was unclear where they could be taken.

The boat is the last private rescue vessel working in the central Mediterranean, and the NGOs asked European governments on Sunday to either reassure Panama that Italy's claims are unfounded, or to issue a new flag so it can keep sailing.

Spain's maritime rescue service said on Sunday that it had pulled 447 refugees to safety off of its southern coast.

A recent spike of refugees entering the country has put Spanish authorities under pressure, which has only worsened with Italy's refusal to allow rescue boats to dock.