Anglican Archbishop Emeritus Desmond Tutu and a group of retired global leaders have joined international leaders in condemning the Israeli forces' raid on a ship delivering relief supplies to Gaza.
"We as elders condemn Israel utterly for this attack. The actions of the Israelis is inexcusable," said Tutu.
He was speaking at the conclusion of a meeting of the group formed in 2008 to highlight humanitarian issues. Members include former UN secretary general Kofi Annan and former US president Jimmy Carter.
Reading a statement, Tutu said the Elders wanted an urgent investigation into the "tragic incident" after Israeli forces boarded the Mavi Marmara as it sailed with a flotilla to Gaza.
He said it should draw the world's attention to the "terrible suffering of Gaza's 1.5 million people, half of whom are children under the age of 18".
The Elders considered Israel's blockage of Gaza illegal collective punishment of its inhabitants and said it was also counterproductive.
"This is because it creates unacceptable suffering, in the process empowering extremists and undermining moderate forces in Gaza", they said.
On Monday morning Israeli forces boarded one of the ships which was violating Israel's blockade on certain goods entering the contested area. Israel warned last week that it would arrest those on board.
News reports said that at least 10 people were killed.
The Israeli Defence Force has said that they had tried to intercept the ships to search them, but were then fired on and attacked with knives and clubs.
Ten civilians were killed and four navy staff were among those injured.
The soldiers had been given full backing by Israeli Prime Minister Benjamin Netanyahu, according to Associated Press.
South Africa's foreign office said it was trying to establish whether there was a South African on board the ship during the attack, which it said should get the "highest level of international condemnation".
The Congress of SA Trade Unions called the incident "state sponsored piracy" and urged a boycott of Israeli products, while the SA Municipal Workers' Union issued a statement on behalf of a large group of civil society organisations calling it a "massacre".
"The convoy of ships was carrying 750 people from 40 different countries including 35 international politicians, members of parliament, former diplomats, human rights activists, aid workers and journalists and was destined for the Gaza port of Rafah later this afternoon.
"The flotilla carried essential aid material, such as medication, construction material, toys, workbooks, chocolate and pasta to Gaza," which the organisations said were banned by Israel.
They said South Africa should immediately recall its ambassador to the capital Tel Aviv, expel the Israeli ambassador in South Africa, and sever diplomatic ties with Israel.
The organisations represented in the statement included the Palestine Solidarity Committee and the Muslim Judicial Council.