ALEXANDRIA, Egypt, June 4 (Reuters) - Thousands of Egyptians demonstrated against Israel's blockade of Gaza on Friday, chanting pro-Hamas slogans in a sign of mounting rancour in the first Arab country to make peace with the Jewish state.

About 20,000 protesters gathered in the port city of Alexandria, waving Egyptian, Turkish and Palestinian flags in response to Israel's a raid on an aid ship bound for Gaza.

The protest, organised by Egypt's most powerful opposition group, the Muslim Brotherhood, was unusual in a country where public demonstrations are often swiftly suppressed.

Hamas, Hamas, you are the artillery and we are the bullets, the protestors chanted, urging the Islamist group which rules Gaza to confront Israel.

Israel sparked global outrage when its military killed nine Turkish activists during the Monday raid. Relations with Turkey have plunged to their lowest since the two countries forged a strategic relationship in the 1990s.

Turkey's diplomatic confrontation with the Jewish state has since boosted its popularity among Arabs who long to see their own governments show similar resolve.

Turkey, a thousand salutations. Long live Erdogan and long live the Turkish people, the protestors chanted in Alexandria, referring to the Turkish Prime Minister Tayyip Erdogan.

This week Egypt, which made peace with Israel in 1979, opened its Rafah border to allow aid convoys into the coastal strip -- a move widely seen as an attempt to deflect criticism of its role in the blockade.

Cairo, coordinating with Israel, has allowed only limited crossing of the border since Hamas took control of Gaza in 2007.

A permanent opening would be a boost for the Islamists, an offshoot of Egypt's Muslim Brotherhood, and a blow to efforts by Israel and its Western allies to cripple them.

The Brotherhood is officially banned but tolerated by the Egyptian government. Its members, running as independents, hold a fifth of seats in the lower house of Egypt's parliament.