At least 15 people were killed and a large number injured
The Secretary-General of the United Nations António Guterres has called for "an independent and transparent investigation" into fatal clashes in Gaza.
A spokesman for Mr Guterres says he is " deeply concerned" on the situation there.
His statement follows clashes at the Gaza fence on Friday between Palestinians participating in the 'Great Return March' and Israeli security forces.
At least 15 people were killed and a large number were injured.
Spokesman Farhan Haq adds: "The Secretary-General calls for an independent and transparent investigation into these incidents.
"He also appeals to those concerned to refrain from any act that could lead to further casualties and in particular any measures that could place civilians in harm's way.
"This tragedy underlines the urgency of revitalizing the peace process aiming at creating the conditions for a return to meaningful negotiations for a peaceful solution that will allow Palestinians and Israelis to live side by side peacefully and in security.
"The Secretary-General reaffirms the readiness of the United Nations to support these efforts."
Tear gas, rubber bullets and live fire are said to have been used by Israeli security forces.
Palestinian President Mahmoud Abbas declared a national day of mourning on Saturday after one of the deadliest days in the region in recent years.
The Israeli Defence Forces alleged there were 'violent riots' along the security fence at the Gaza Strip - claiming protesters were rolling burning tires and throwing stones at the fence and troops.
Around 20,000 people are believed to have attended the demonstrations, in support of refugees expelled from their homes.
The march began on March 30th to mark Land Day - a day of commemoration to mark the deaths in Israel of six unarmed Arab protesters in 1976.