GAZA CITY — Young Palestinians in the Gaza Strip ferried carts of tires to the fence with Israel on Thursday, stacking them to be burned in a demonstration dubbed the ‘‘Friday of Tires’’ and sparking concerns of violence a week after the bloodiest day in Gaza since a 2014 war.

At a demonstration point near Gaza City, protesters began burning the tires on Thursday afternoon, with rock-throwers taking cover behind the thick billowing black smoke. Israeli forces used gunfire and tear gas to keep them away from the border fence.

Hamas, the militant group that controls Gaza, and other major Palestinian factions have thrown their weight behind demonstrations in the 140-square-mile territory on the Mediterranean Sea. Eighteen Palestinians were killed when Israeli forces opened fire on a crowd that massed on the border for a demonstration called the ‘‘March of Return’’ last week on Land Day, an annual commemoration of a 1976 protest against Israeli confiscation of Arab-owned land.

Israel has said the crowd was violent and that Hamas has tried to use the demonstrations as cover to carry out attacks.

While most of the crowd was peaceful on Friday as more than 30,000 Palestinians gathered near the dividing line with Israel, groups of young men threw rocks and molotov cocktails toward the fence.

Nickolay Mladenov, the UN special coordinator for the Middle East peace process, said he was following rhetoric and preparations for Friday’s planned march ‘‘with concern.’’

‘‘Israeli forces should exercise maximum restraint, and Palestinians should avoid friction at the Gaza fence,’’ he said.

The Israeli human rights group B’Tselem launched a campaign calling on Israeli soldiers not to fire at unarmed demonstrators on Friday, taking out advertisements in newspapers.