Thousands of protesters took to the streets of Istanbul and London today over the killings of nine Turkish activists aboard a flotilla of aid ships bound for Gaza.

Anger in Turkey over last week’s deaths showed no sign of abating as leaked post-mortem results showed that the activists were killed by a hail of 9mm bullets, many fired at close range. Five of the nine were shot in the head.

The Turkish attorney general’s office said it was collecting witness statements with a view to attempting legal action against Israeli leaders.

In London, thousands joined a march from Downing Street to the Israeli embassy to express “outrage” at the killings. They also protested against the boarding of the MV Rachel Corrie, another aid ship trying to break the Israeli naval blockade of Gaza, by Israeli forces this morning.

Demonstrators outside No 10, many from London’s Turkish community, waved Palestinian flags and placards saying: “Gaza End The Siege” and “For Freedom We Sail”. Others chanted: “Stop Israeli piracy”.

Among the London protesters was Sarah Colborne, 43, who was on board the Turkish ship Mavi Marmara when it was stormed by an elite Israeli unit with tragic consequences.

Lindsey German, from Stop the War Coalition, said the event was to show that victims’ “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”.

In Istanbul some 5,000 people took to the streets, gathering at Caglayan on the European side of the city for a protest organised by the charity Foundation of Humanitarian Relief (IHH), a key organiser of the flotilla.

Protesters hoisting a banner reading, in French, “The longer we keep silent, the bigger the massacre grows.”

Others waved Palestinian flags and shouted anti-Israeli slogans. Many expressed support for Hamas, the Islamist group which governs the Gaza Strip.

Rallies also took place across Canada, urging the country’s Prime Minister, Stephen Harper, to condemn Israel’s actions.

Leaked reports from the post-mortem examinations of the nine dead Turkish activists, one of whom also held a US passport, showed the men had been shot a total of 30 times, and five of them were killed by gunshot wounds to the head.

One 60-year-old man, Ibrahim Bilgen, was shot four times in the temple, chest, hip and back. Fulkan Dogan, 19, the holder of a US passport, was shot five times, all from a range of less than 45cm.

The chairman of the British pro-Palestinian group Friends of al-Aqsa, Ismail Patel, said he had witnessed some of the shootings and believed Israel had pursued a “shoot to kill policy”. He said 48 people were suffering from gunshot wounds in addition to the nine dead.

Israel maintains its soldiers shot only in self-defence, and accounts have emerged of a small group of activists attempting to kidnap Israeli soldiers during the confrontation on the Mavi Marmara. A single Israeli commando who killed six of the activists is being considered for a medal of valour.

However, before the arrival of the MV Rachel Corrie this morning – an Irish ship that had originally been scheduled to travel with the Mavi Marmara and the rest of the flotilla – Israel’s Prime Minister, Binyamin Netanyahu, was reported to have told Israeli soldiers to avoid harming those on board.