Irish activists supporting a new bid to break Israel's blockade of the Gaza Strip urged their government on Thursday to seek Israeli assurances that a new aid flotilla would be allowed free passage.

The two vessels, the Irish Saoirse (meaning Freedom) and the Canadian Tahrir (Liberation in Arabic) which are carrying 27 people, are south-west of Cyprus and expect to reach Gaza by Friday, the activists told a press conference in Dublin.

Claudia Saba, a spokeswoman for the Irish Ship to Gaza group, said the activists had called on the Irish foreign ministry to tell Israel not to impede the vessels.

"All Ireland has to do to ensure Irish citizens are not attacked and not approached in any way, seeing as they are never going anywhere near Israeli waters, is to say: 'If you want to maintain good trade and diplomatic relations with us then do not dare touch our citizens'," Saba said.

Padraig Mac Lochlainn, foreign affairs spokesman for the small opposition Sinn Fein party which has representatives on the Irish ship, also called on the government "to speak to the Israeli government and seek safe passage".

A spokesman for the Irish foreign ministry told AFP it was in contact with the flotilla organisers and the Israeli authorities, adding: "Our chief concern is the welfare of the Irish citizens who are travelling on the flotilla.

"We are acting to try and ensure to the greatest degree possible that we do not have any repeat of any incident such as what happened on the first flotilla."

In May 2010, Israeli naval commandos raided a flotilla of ships trying to sail to Gaza, killing nine Turkish activists and sparking a diplomatic crisis.

A second flotilla tried to reach the Palestinian territory in July but several ships were sabotaged and the rest were intercepted before they arrived.

Irish activists accused Israel of sabotaging their ship and Dublin said it would take a "very serious view" if sabotage were proved.

Saba said the Saoirse was carrying 15 passengers but no aid, while there is about $30,000 worth of medical aid on the Tahrir.

Israel has vigorously defended its right to maintain a blockade on Gaza, saying it is necessary to prevent weapons from entering the coastal territory.