A flotilla of eight boats carrying thousands of tonnes of construction materials, medical equipment and other aid is preparing to sail to Gaza in the next few days, setting the scene for a confrontation with Israel which has vowed to prevent the ships breaking the blockade on the Palestinian territory.

Three cargo ships and five passenger vessels plan to meet up in international waters between Cyprus and Gaza Strip before heading towards Gaza City. The Israeli military is expected to stop the flotilla and divert it to the Israeli port of Ashdod.

One of the organisers of the flotilla, which includes three vessels from Turkey, is IHH, a humanitarian aid group supported by Ankara. Diplomatic relations between Turkey and Israel have deteriorated since the Israelis launched a three-week war on Gaza in 2008-09. An attempt to block the flotilla is likely to increase tensions between the two countries. The Turkish prime minister, Racep Tayyip Erdogan, has called on Israel to avoid this be allowing the boats through.

"This could make relations between Israel and Turkey more complicated," said Yigal Palmor, an Israeli foreign ministry spokesman.

On board the ships are 10,000 tonnes of cargo and about 700-800 activists and politicians from more than 40 countries. The cargo includes building materials, medical supplies and paper for schools. One boat is carrying a complete dental surgery including drills. Crayons and chocolate are also on board for Gazan children. The cargo has been paid for by donations.

"We're trying to break the blockade of the Gaza Strip and tell the world that Israel has no right to starve 1.5 million Palestinians," said Greta Berlin, of the Free Gaza Movement, another organiser of the flotilla. "We are bringing in vitally needed supplies so the people of Gaza can rebuild their infrastructure."

Israel has imposed an economic blockade on Gaza since the Palestinian Islamist movement Hamas seized control almost three years ago. Nearly all exports and imports are banned and only a limited supply of food and medical aid is allowed in.

Free Gaza has organised six previous aid boats to the Palestinian territory, the last three of which were blocked from reaching their destination by the Israeli military. This is the biggest attempt to take aid to Gaza. "The previous boats were making a statement ‑ these boats will be making a real impact," said Berlin.

The Israeli navy enforces a 20-nautical mile (23-mile) closure of the sea off Gaza, which has had a devastating impact on its fishing industry. "The boats will not be allowed to enter Gaza territorial waters," said Palmor. "This is a territory in a self-declared state of war with Israel. There can be no uncontrolled transportation in or out of Gaza."

Berlin accused Israel of "sabre-rattling" in the hope that the flotilla plan will be abandoned. "They have no right to control Gaza waters unless they want to admit they are occupying Gaza," she said. "They are the illegal entity, not us." Israel claims it is acting within international law.

The Turkish ferry Mavi Marmara was today docked in Antalya, Turkey, along with two cargo ships, waiting to be joined by boats from Greece. "We will all go together in the next couple of days," said Hosain Orut, of the IHH.

John Ging, head of the main UN agency in Gaza, urged more ships carrying aid to be sent: "We believe that Israel would not stop these vessels because the sea is open, and many human rights organisations have been successful in previous similar steps, and proved that breaking the siege on Gaza is possible."

Earlier this week, a UN report said that three-quarters of the damage caused to Gaza's infrastructure during the three-week military conflict has not been repaired because of the blockade.

Mark Regev, the Israeli prime minister's spokesman, said: "It is strange that human rights activists are acting as apologists for a regime that is brutally repressing human rights. Hamas oppresses women, gays and Christians, has crushed independent media and destroyed all political opposition." He added that 15,000 tonnes of aid was allowed into Gaza every week.

Dozens of boats manned by Israeli citizens took the water at the weekend in protest at the aid flotilla.

The boats

• Four cargo ships

• Four passenger ships

• Coming from Turkey, Greece, Ireland

On board

• 700 to 800 peace activists and MPs from more than 40 countries

• 10,000 tonnes of supplies, including:

• Cement

• Generators

• Water purification equipment

• 20 tonnes of paper for schools

• Prefabricated homes

• $1m (£700,000) of medical equipment, including: CAT scanners' wheelchairs, crutches

• A complete dental surgery, including drills and a chair

• Sports equipment, including footballs and basketballs

• Crayons and pens

• Chocolate

Paid for

• By donations, ranging from $1.39 from an individual in Brunei to €300,000 (£256,000) collected in Malaysia

Follow the flotilla witnessgaza.com