* Spanish charity rescued migrants off Libya more than 2 weeks ago
* Italian minister Salvini has refused to let ship dock
* At PM's insistence, 27 minors to be allowed off
* League chief Salvini is trying to bring down govt
By Guglielmo Mangiapane and Joan Faus
LAMPEDUSA/BARCELONA, Aug 17 (Reuters) - A charity that operates a rescue ship carrying 134 migrants off the coast of Italy said on Saturday that it could not guarantee their security, after the boat had spent more than two weeks waiting for a port to disembark in.
The migrants picked up off the coast of Libya, most of whom are African, are waiting to disembark on the southern Italian island of Lampedusa.
Italy's far-right Interior Minister Matteo Salvini has ordered his officials not to let them do so, although on Saturday he made a partial concession, saying he would allow any children to leave the boat. He added that he had only agreed to this at the insistence of Prime Minister Giuseppe Conte.
The Barcelona-based NGO Open Arms said that 27 minors were to be allowed off the boat.
It also said that the 16 days waiting for a port to disembark in had taken their toll on the migrants, with frequent fights breaking about among them and conditions on board deteriorating.
"After ... six medical evacuations and having told authorities about our situation without receiving an answer, we are in a situation of need and we cannot guarantee the security of the 134 people onboard," Open Arms said.
"It is terrible, the things that are happening are not only physical but psychological. The conditions in which they were staying in Libya and now in the ship, it is just terrible, with 130 people and two toilets," Open Arms' director and founder Oscar Camps told Reuters on Friday.
France, Germany, Romania, Portugal, Spain and Luxembourg have said they will help relocate the migrants, but the reaction from Salvini's interior ministry has been sceptical.
Salvini issued a statement on Saturday reiterating that Open Arms could have taken the migrants to Spain and that it was to blame for their plight. But he added that he was now willing to allow "presumed minors" off the boat.
Salvini, leader of the ruling League party, has built his popularity on a vigorous campaign against illegal immigration.
On Aug. 8, in an apparent attempt to capitalise on his surging voter support, he announced his ruling coalition with the anti-establishment 5-Star Movement was no longer workable and called for elections that could crown him as prime minister.
However, his move has not gone to plan.
Conte, who is not a member of either ruling party, has accused him of disloyalty and of using immigration for political gain, while parliament has so far refused to discuss a motion of no-confidence in the government put forward by the League.
"Permission to disembark for these people is the sole responsibility of Prime Minister Conte," Salvini said, insisting that "the great majority of Italians" shared his own hard-line stance in closing Italy's ports to charity ships.
5-Star said Salvini no longer had the right to act as interior minister and called on him to resign.
Camps blamed politicians for the standoff.
"This isn't a game, it is a provocation, I don't know what you would call it, but we are waiting for a solution. We want an end to this because it is a sanitary emergency. These people who have been left outside, need help," he said.
The NGO's director said on a video from the boat released on Saturday that there are constant fights on board and the tension is unsustainable.
Citizens of Eritrea, Somalia, Nigeria and Cameroon are among those on board, a spokeswoman for Open Arms said.
The Open Arms boat was allowed into Italian waters on Thursday after an administrative court in Rome overruled a ban on its entering that Salvini had previously imposed. (Additional reporting ad writing by Gavin Jones; Editing by Hugh Lawson)