Italian authorities have ordered the seizure of a migrant rescue ship operating in the Mediterranean.

Médecins Sans Frontières (MSF) - one of the organisations which operates the ship - says judicial authorities have requested the seizure of the Aquarius vessel "for alleged anomalies in its disposal of on-board waste".

Italian media reports that prosecutors in Catania are alleging that 24 tonnes of hazardous waste were illegally disposed of.

It comes amid an ongoing crackdown by the Italian government against immigration.

The Aquarius is the last private search and rescue vessel operating in the Mediterranean, and has previously had its registration revoked by Panama following apparent pressure from Italy.

Responding to the seizure order, Italian interior minister Matteo Salvini claimed: "I did well to block the ships of the NGOs, not only did I stop the traffic of illegal immigrants but, as it emerges, also that of toxic waste."

Gabriele Eminente, General Director of MSF in Italy, suggested there have been two years of "smear campaigns" against search and rescue activities in the Mediterranean.

He observed: "We are more than ready to clarify the facts and stand accountable for the operational procedures we followed, but we strongly reaffirm the legitimacy and legality of our humanitarian work.

"This climate of repeated attacks and baseless accusations has led to the real crimes we see today at sea. This year alone, more than 2,000 people have perished in the Mediterranean, while still others continue to take the dangerous sea journey with no dedicated search and rescue vessels left to save their lives."

SOS Méditerranée, which runs the Aquarius along with MSF, also strongly condemned the move.

Head of Operations Frederic Penard said: "The tragic current situation is leading to an absence of humanitarian search and rescue vessels operating in the central Mediterranean, while the mortality rate is on the rise."