The Israeli military has defended its handling of clashes in Gaza which left 16 Palestinians dead even as footage emerged appearing to show unarmed protesters being shot by Israeli snipers.

Palestinian mourners called for "revenge" as they buried their dead after the bloodiest day in Gaza since the 2014 war and both side braced for what is expected to be weeks of rolling protests.

Around 30,000 Palestinians marched towards the Israeli border on Friday, where some hurled rocks and burning tyres and Israeli troops opened fire with live ammunition.

António Guterres, the UN secretary general, called for an investigation into the killings.

The Israeli Defence Forces (IDF) said that its forces had fired only at specific people who were deemed to be “violent instigators” in the demonstrations.

“The use of snipers was against specific people who were specific perpetrators of violence,” said Lt Col Peter Lerner, an IDF spokesman.

However, widely shared videos on social media appeared to show at least two unarmed men by Israel gunfire.

Three separate clips were published on social media purporting to show one Palestinian shot as he walked towards the border the Israel.