As Palestinian militants fired mortar shells into southern Israel and Israeli forces responded with airstrikes on Gaza targets on Tuesday, a group of Palestinians launched a humanitarian envoy of fishing boats off the Gazan coast to challenge Israel and Egypt's naval blockade.

A main boat carrying about 20 people set sail from the Gaza City harbor on Tuesday, accompanied by several smaller vessels, said protest organizers and AFP journalists.

"Occupants include medical patients and students unable to leave through overland crossings," according to the Associated Press.

The Israeli navy, which has imposed the blockade for more than a decade, seized control of at least one boat that attempted to cross the blockade. An organizer told the AFP "Israeli forces surrounded it and intercepted it," and that organizers had lost communication with the vessel for more than 30 minutes.

Initially, reports Raidió Teilifís Éireann, "there were conflicting statements about whether the boats would seek to break Israel's blockade, which currently allows them to travel nine nautical miles (16km) off the coast. Some organizers said they would only protest, while other participants said they wanted to move past the limit."

The expedition, as the AP noted, "marks eight years since Israeli commandos raided a Gaza-bound aid flotilla, killing nine pro-Palestinian Turks and sparking an international outcry against the blockade."