The charity ship Lifeline is seen at Boiler Wharf in Senglea, in Valletta's Grand Harbour, Malta June 27, 2018. REUTERS/Darrin Zammit Lupi

VALLETTA (Reuters) - Malta said on Thursday it would allow no more migrant rescue boats run by non-governmental organizations (NGOs) to enter its ports, as a European Union summit meeting began in Brussels with immigration top of the agenda.

On Wednesday Malta let the charity ship Lifeline dock in Valletta with 230 migrants on board, after it was stuck at sea for almost a week after Italy closed its ports to NGO rescue vessels.

However, Maltese Prime Minister Joseph Muscat said the gesture was a one-time “ad-hoc” resolution to the crisis.

Maltese authorities are investigating Lifeline’s crew for not following instructions from Italian authorities to leave the migrants, at sea in flimsy boats, to be intercepted by the Libyan coastguard.

“Malta cannot allow entities, whose structure might be similar to that being subject to investigations, to make use of Malta as their port of operations,” the government said in a statement on Thursday.

It said its decision to bar humanitarian ships was to avoid being “considered to be approving of systems of operations that might eventually be found to be carried out in breach of their own and international rules”.

Lifeline is the second charity ship that Italy has shut out of its ports this month after the new anti-immigrant Interior Minister Matteo Salvini said private rescue vessels would no longer be welcome because they “cannot dictate Italy’s immigration policy”.

Salvini said Malta’s decision showed Italy had been right to shut its own ports to NGOs, which he accuses of helping people traffickers.

“There is no turning back,” he said on Facebook.