Palestinians in Gaza have marched in thousands to the Israeli border at the start of a six-week-long protest.
The Palestinian health ministry says at least five people have been killed and 350 wounded, many of them by Israeli gunfire.
The Israeli military reported "rioting" at six places and said it was "firing towards main instigators".
Palestinians have pitched five camps near the border for the protest, dubbed the Great March of Return.
The Israel Defense Forces (IDF) said there were about 17,000 Palestinians in five locations along the border fence.
The IDF said troops were "firing towards the main instigators" to break up rioting that included the burning of tyres and the throwing of Molotov cocktails and stones at the fence.
The IDF said it had "enforced a closed military zone" in the area surrounding Gaza.
Palestinian health officials said that before Friday's protest started, 27-year-old farmer Omar Samour had been killed by Israeli tank fire near Khan Yunis.
Another man was injured.
Witnesses say the two men were collecting parsley in a field, reports BBC.
Hamas, the militant group that dominates the Gaza Strip, has accused Israel of trying to intimidate Palestinians by killing the farmer and by urging them not to participate in the protests.
Addressing protesters, Hamas senior political leader Ismail Haniyeh said "we will not concede a single inch of the land of Palestine".
The Jerusalem Post also reported a rare public appearance by the leader of Hamas in Gaza, Yehiya Sinwar.