The crowd gathered at Caglayan on the European side of the city straddling the Bosphorus Strait at the call of Foundation of Humanitarian Relief (IHH), one of the key organizers of the aid flotilla to the Gaza Strip.

“The longer we keep silent, the bigger the massacre grows,” read a banner in French while the demonstrators waved Palestinian flags and shouted anti-Israeli slogans.

There have been daily demonstrations across Turkey against Israel and in favor of Hamas since Monday when Israeli commandos stormed the aid fleet.

In London, several thousand people gathered outside Downing Street on Saturday for an angry protest against the killing of activists by Israeli forces. Waving flags and placards and chanting loudly, protesters urged the British government to step up pressure on Israel following the deadly commando raid on the Gaza-bound ships.

Lindsey German of organizers Stop The War Coalition told the crowd the event was to show victims “that their death has not been in vain — what it has done is bring to the world’s attention the terrible crime of the blockade of Gaza.”

Demonstrators outside the prime minister’s residence waved Palestinian flags and waved placards saying: “ End Gaza Blockade, “For Freedom We Sail”, while others chanted: “Stop Israeli piracy.”

Many of those attending were from London’s large Turkish community such as 38-year-old Ali Seylan who said his brother had been on board the flotilla.

“Thank God nothing happened to my brother — had if anything happened to him I was going to get my revenge myself,” he said.

He said many London-based Turkish people had joined the march.

Sami Mehmet, 65, who lives near London but is originally from Cyprus, described Israel’s behavior as piracy. “I want (British Prime Minister David) Cameron and his colleagues and the rest of the EU to take notice and bring Israel to book because they have been doing it for far too long,” he said. Asked what the mood was like of people on the march, he added: “They’re very angry, rightly so. I’m angry but I don’t shout because I’m not well. I wish I could shout”.