Jerusalem (CNN) -- Israel has attempted to deliver humanitarian aid from an international flotilla to Gaza, but Hamas -- which controls the territory -- has refused to accept the cargo, the Israel Defense Forces said Wednesday.

Palestinian sources confirmed that trucks that arrived from Israel at the Rafah terminal at the Israel-Gaza border were barred from delivering the aid.

Ra'ed Fatooh, in charge of the crossings, and Jamal Khudari, head of a committee against the Gaza blockade, said Israel must release all flotilla detainees and that it will be accepted in the territory only by the Free Gaza Movement people who organized the flotilla.

Israel said it had 20 trucks of aid found on the ships, such as expired medications, clothing, blankets, some medical equipment and toys.

Israel has released all foreign flotilla detainees by Wednesday, but four Israeli Arabs remain in custody.

Nine people died Monday when Israel intercepted an aid vessel bound for Gaza.

Under Israeli policy, humanitarian aid must come through Israel and be checked by Israeli authorities who are looking to intercept smuggled weapons bound for militants aiming to attack Israel.

As part of this policy Israel forbids ships from dropping off goods at Gaza ports and works to thwart smuggling via tunnels between Gaza and Egypt.