Silences have been held around Britain to mark 40 years since 11 Israeli athletes were murdered during the 1972 Munich Olympics.

More than 20,000 people joined the Zionist Federation organised "Minute for Munich", a virtual silence conducted by individuals wherever they were at 11am, that had been promoted on social media.

A short memorial service at the Israeli Embassy and planned by the ZF was streamed live online from 10.45am, in which the memorial prayer was recited and memorial candles were lit.

Around 200 people marked the Minute for Munich in Trafalgar Square. In front of journalists and television crews from around the world they waved British and Israeli flags before observing the minute's silence.

The event was organised by the British Israel Coalition and other Israel advocacy groups. BIC's Ari Soffer told the crowd: "The British Jewish community is showing its solidarity with our brothers and sisters in Israel.

"We should not allow this tragedy to go un-commemorated. This is a time to show our respect and remember the dead."

During the short service the crowd recited memorial prayers including El male Rachamim and the names of the murdered Israelis. Following the minute of silence kaddish was said, followed by the singing of the British and Israeli national anthems.

A Swedish tourist, Joseph, said he felt it was important to attend: "I escaped from Poland to move to Sweden and it's natural for us, as Jews, to show solidarity with Israel.

"The IOC decision not to hold a silence during the opening ceremony is terrible. It's unbelievably arrogant and ignorant. They have not done it out of antisemitism, but for political reasons.

"I think this was a beautiful moment to remember the murdered athletes."

Londoner Moishe Fehler, 17, said: "I feel connected to Israel and I wanted to remember the Munich 11. It's disgusting that the IOC has not done anything – the ceremony at the Athletes' Village on Monday was kept quiet until afterwards."

Dov Ibgi added: "The IOC did not tell anyone about Monday until it was over. I don't know why they couldn't find just one minute in the opening ceremony."

The silences came two days after the IOC president Jacques Rogge again refused to allow a minute's silence at today's Opening Ceremony of London 2012, despite being asked directly by two of the women widowed in the massacre.

"We believe it is wrong that the IOC refuses to commemorate the Munich massacre at the Opening Ceremony," said Alan Aziz, the ZF's executive director. "We must not let people forget and the groundswell of support that our campaign has received has demonstrated that not only do people remember the horrific events of Munich, but they also understand the importance of remembering it and the innocent victims of that fateful day."