* Turk activists killed by Israeli marines in 2010 flotilla
* Israel dismisses plan for new sailing
* Activists' plan may further hamper Turkey-Israel ties (Adds comment from Israeli official, updates Gaza death toll)
ISTANBUL, Aug 12 (Reuters) - Pro-Palestinian activists said on Tuesday they would send ships this year to the Gaza Strip to try to breach Israel's naval blockade, repeating an action that four years ago ended with Israeli marines boarding a vessel and killing nine Turks.
The Freedom Flotilla Coalition, made up of 10 rights groups from 10 countries, did not specify how many ships would sail or when. Israel views the Istanbul-based Humanitarian Relief Foundation (IHH), a leading participant, as a terrorist group.
"It is the responsibility of civil society to challenge this blockade ... We plan to sail to Gaza during 2014," said Ann Ighe, a Swedish spokeswoman for the coalition, after a meeting in Istanbul of pro-Palestinian activists from 10 countries.
Israel, which is in Egyptian-mediated talks with Gaza's dominant Hamas Islamists to end a month-old war, brushed off the activists' plan and signalled the blockade would be enforced.
"They have got nothing to do with human rights or humanitarian assistance. They are interested in pursuing conflict," said Paul Hirschson, a Foreign Ministry spokesman, noting previous flotilla announcements had not been carried out.
"The naval blockade has been ruled legal and legitimate by the United Nations. It is there because of terror against the Israeli public."
Earlier this year, Turkish anti-terrorist police raided the offices of IHH, the main agency through which Turkey channels aid to Syria, in a move the group said was a ploy to tarnish it. The IHH denied media reports at the time that it was involved in arms shipments to al Qaeda-linked groups in Syria.
In 2010, the IHH led a flotilla, including the cruise ship Mavi Marmara, that was carrying humanitarian aid when it was stopped in international waters by the Israeli navy.
Marines stormed Mavi Marmara and killed nine Turks in deck clashes. A 10th person died this May from wounds sustained in the incident, which wrecked already-damaged relations between Israel and Turkey, once Middle East allies.
A U.N. inquiry appointed by Secretary-General Ban Ki-moon faulted Israel for excessive force against the Mavi Marmara but also found the Gaza blockade to be a lawful means of preventing weapons from reaching the Palestinian enclave's militants.
The activists will not seek support from the Turkish government, such as for a military escort, because it is a non-governmental mission "committed to non-violence", said Dror Feiler, an Israeli-born Swedish citizen who took part in the 2010 effort.
The plan may hinder efforts to rebuild the Turkish-Israeli relationship, just as Ankara launched an "air corridor" carrying wounded Palestinians to Turkey and aid to Gaza.
Turkish Prime Minister Tayyip Erdogan, elected president on Sunday, has been among the most vocal critics of Israel's current conflict with Hamas - fighting that has killed 1,939 Palestinians, mostly civilians, as well as 64 Israeli soldiers and three civilians in Israel.
The group said the proposed flotilla would travel to Gaza to collect commercial goods purchased from the occupied territory.
(Reporting by Ayla Jean Yackley and Dan Williams; Editing by Alison Williams)