An armada of Palestinian fishing boats that sailed from Gaza to challenge an Israeli naval blockade has drawn warning shots from the Israeli navy, the fleet’s organisers say.

About 20 fishing boats set sail from Gaza City on Saturday toward the maritime border with Israel. The Gaza Health Ministry said there were no casualties.

An Israeli military spokeswoman said the navy gave the boats verbal warnings before firing into the air.

Palestinian witnesses said some of those on board set tyres alight and set them afloat toward the maritime border before they were confronted by four Israeli naval vessels.

Israel says its naval blockade of Gaza is intended to prevent weapons from reaching militant groups, including Hamas, the Islamist movement that controls the Palestinian enclave. Israel and the West designate Hamas as a terrorist organisation.

More than two million Palestinians are packed into the Gaza Strip, which is experiencing deep economic hardship.

Israel and Egypt, citing security concerns, keep tight restrictions on their land crossings with Gaza which have reduced its economy to a state of collapse.

UN and Egyptian-led efforts are under way to mediate a long-term ceasefire between Israel and Hamas who have fought three wars since 2008. The bid is also meant to tackle humanitarian issues in Gaza and improve its economy.

Adham Abu Selmeya, one of the flotilla organisers, said the event was meant to send a message to all parties involved in the ceasefire efforts.

“We want the world to see the reality of the blockade and the suffering of the people of Gaza, and we will not accept anything less than lifting the blockade once and for all,” he said.

Cross-border violence has spiked in the past few months. Since the weekly protests began on March 30, the Israeli army has killed 161 Palestinians and a Gaza sniper has killed an Israeli soldier.

On Thursday, Egyptian mediation ended a two-day wave of rocket barrages and air strikes between Israel and Gaza militant groups.