The NGO migrants' rescue ship Sea Watch IV, carrying some 200 migrants on board, on Thursday sailed close to the tanker Maersk Etienne as both vessels search for a safe port to disembark those on board.

The Etienne has been stranded on Hurd's Bank, just outside Malta's territorial waters for three weeks, having rescued 27 migrants including a baby earlier this month.

The Sea Watch IV picked up some 200 migrants in three rescue operations off Libya earlier this week.

Alarm Phone, the NGO which raises the alarm whenever migrant boats call for help, said on Wednesday that the standoff involving the tanker was the longest ever.

"They are imprisoned at sea as Malta denies disembarkation. Never before has such cynical standoff taken that long," it tweeted.

A representative of Danish Shipping, a grouping which includes the tanker's owners, told Times of Malta last week that efforts were underway to reach an  amicable solution. "The situation is totally unacceptable as our vessel has become embroiled in a political struggle which is not of its own doing,” she said.

The European Court of Human Rights on Wednesday dismissed an application for an interim measure for the migrants on board the tanker to be disembarked in Malta.

Writing on Twitter, human rights activist Marc Tilley said that the court had found that "Malta’s decision (not to let the migrants in) does not put these people at risk of inhuman treatment and therefore the safety of these people is not threatened". 

The crew of the Sea-Watch 4 said they had sailed by the Etienne on Thursday to show their solidarity with the vessel and those on board.   

Correction August 28: A quote by Marc Tilley was previously incorrectly attributed to the ECHR.