The UN High Commissioner for Human Rights joined calls for an “immediate and credible” inquiry into the interception and urged Israel to lift its blockade of the Gaza Strip.

The Palestinian delegation formally asked the 47-member UN Human Rights Council to hold a special session on Tuesday afternoon to discuss the incident, a spokeswoman for the council said.

But Israeli ambassador Aharon Leshno Yaar urged the council “not to rush to conclusions.”

The aid vessels were on the last leg of a high profile mission by pro-Palestinian activists to deliver some 10,000 tonnes of supplies to Gaza as part of a protest against Israel’s blockade of the territory since 2007.

“We need to establish exactly what happened. However, nothing can justify the appalling outcome of this operation, which reportedly took place in international waters,” said Pillay.

“I unequivocally condemn what appears to be disproportionate use of force, resulting in the killing and wounding of so many people attempting to bring much-needed aid to the people of Gaza, who have now been enduring a blockade for more than three years.”

Pillay had earlier told the Human Rights Council that she was shocked that the convoy was “met with violence”.

But Israel’s ambassador told the council that numerous warnings were given, and that offers were repeatedly made for the ships to land in the port of Ashdod so that the aid supplies could be transferred overland to Gaza.

As Israel’s offers were rejected, “it was decided that Israeli forces would board the ships and lead them to Ashdod,” said Yaar.

“We do know there was only one ship of six where violence ensued… the organisers’ intent was violent, their method was violent, and unfortunately the results were violent.

“We will certainly brief the council on more specifics as they become available to us. I urge you not to rush to conclusions before that information is known to all of us,” added the Israeli envoy.

Pillay also reiterated her concerns about the impact of the Israeli blockade on human rights in the Palestinian territory ruled by the Islamist Hamas movement.

“The blockade lies at the heart of so many of the problems plaguing the Israel-Palestine situation, as does the impression that the Israeli Government treats international law with perpetual disdain,” she said.

“If the blockade had been lifted, there would be no need for flotillas like this,” Pillay added.

Israel had said the attempt to break the Gaza blockade, imposed since Hamas was elected, was illegal and warned that it would intercept the ships and detain the activists.

It labelled the convoy a media stunt and a provocation, insisting the humanitarian situation is stable in Gaza despite reports to the contrary from aid agencies.