NICOSIA, May 30 (Reuters) - A six-ship convoy carrying 10,000 tons of aid for Palestinians set sail for Gaza on Sunday in defiance of an Israeli blockade on the impoverished territory and warnings that it would be intercepted.

The ships, led by a Turkish vessel carrying 600 people, left a muster point in international waters off Cyprus early on Sunday. There was no estimated time for arrival in Gaza, which lies some 230 miles southeast of Cyprus.

The flotilla is together and is on the move, said Greta Berlin, spokeswoman for the Free Gaza Movement, one of the organizers.

Israel has already said it will prevent the convoy from reaching Hamas-ruled Gaza, a sliver of desert territory which Israel has blockaded for three years.

Israeli naval commandos have held drills to practice boarding and searching the ships.

Activists face arrest and deportation, and their cargo will be confiscated for possible transfer by Israel to Gaza, Israeli military officials said.

Berlin said Israel risked a public relations disaster if it tried to intercept the activists. The only scenario which makes any sense is for them to stop being the bully of the Middle East and let us go through, she said.

The flotilla was organized by pro-Palestinian groups and a Turkish human rights organization. Turkey has urged Israel to allow it safe passage and say the aid is humanitarian.

Muslim Turkey is one of Israel's closest allies in the Middle East but relations have soured. Turkish Prime Minister Tayyip Erdogan has frequently criticized the Jewish state's policies toward the Palestinians.

Israel and neighboring Egypt closed Gaza's borders after Islamist Hamas, which rejects the Jewish state, took over the territory in 2007. Tension has remained high since Israel's devastating December 2008-January 2009 offensive in Gaza.

Gaza's people, many of whom rely on United Nations aid, suffer shortages of water and medicine.

Israel has set up a holding camp for activists at the coastal city of Ashdod and said that any aid should be handed over for screening before being distributed in Gaza through Israeli-approved channels. (Reporting by Michele Kambas, editing by Tim Pearce)