David Cameron has paid tribute to the 11 Israeli Olympic athletes killed in 1972 by Palestinian gunmen in Munich, describing it as "one of the darkest days" in Games history.

The prime minister was attending a memorial service at London's Guildhall, along with widows of those killed, cabinet ministers, Israeli embassy officials and Olympic chiefs.

The event is bittersweet for Munich widows Ankie Spitzer and Ilana Romano, who had campaigned tirelessly to have the silence included in the official Olympic opening ceremony, but were denied by International Olympic Committee president Jacques Rogge.

Cameron told guests at the ceremony: "As the world comes together in London to celebrate the Games and the values it represents, it is right that we should stop and remember the 11 Israeli athletes who so tragically lost their lives when those values came under attack in Munich 40 years ago.

"It was a truly shocking act of evil. A crime against the Jewish people. A crime against humanity. A crime the world must never forget.

"We remember them today, with you, as fathers, husbands, and athletes, as innocent men, as Olympians and as members of the people of Israel, murdered doing nothing more and nothing less than representing their country in sport."

Cameron said the UK was a "staunch friend" of Israel and will work with it to tackle terrorism.

"We remember too the six Israeli holidaymakers brutally murdered by a suicide bomber in Bulgaria just last month.

"And let me say that we in Britain will do everything we can in helping to hunt down those responsible for that attack.

"Britain will always be a staunch friend of Israel. And we will stand with the Jewish people and with all victims of terror around the world, whoever they are and wherever they are from.

"Seven years on from 7/7 I am proud that as we speak, this great city of London - probably the most diverse city in the world - is hosting athletes from 204 nations.

"And I am delighted that a strong Israeli team is among them."

The event was organised by the National Olympic Committee of Israel, the Jewish Committee for the London Games and the Embassy of Israel.

Labour leader Ed Miliband also spoke at the event, which was attended by Rogge, Locog chair Lord Coe, Mayor of London Boris Johnson and Culture Media and Sport Secretary Jeremy Hunt.

Opinion has been divided over whether a memorial for Israeli athletes killed by Palestinians would have "politicised" the opening ceremony.

The two widows, whose husbands Andrei Spitzer and Yosef Romano were killed after being taken hostage by Palestinian Black September terrorists at the Munich Olympic village, handed a petition with 105,000 signatures to Rogge pleading with him to mark the 40th anniversary of the murders at the opening ceremony.

Spitzer told The Huffington Post UK: "Rogge was an athlete in 1972. I told him that him and my husband had the same dreams, but my husband came home in a coffin and Rogge went to be president of the IOC."

The widows have been unhappy that the memorial was not organised by Olympic officials, and takes place away from the Olympic Park, "out of sight".

Last week, it was reported that the Palestinian Olympic delegation's Jibril Rajoub reportedly thanked IOC president Jacques Rogge for denying the families of the victims a silence.

“Sports are a bridge for love, communication and the spreading of peace between nations and should not be used for divisiveness and the spread of racism,” he wrote, according to the Times of Israel.

Rogge held a spontaneous minute's silence, in the athlete's village, at the signing of the Olympic Truce, the first time such a memorial has been held at an Olympic venue since the massacre.

The IOC president said it was to honour "the Israeli Olympians who shared the ideals and have brought us together in this beautiful Olympic Village".

He added: "As the event of 40 years ago reminds us, sport is not immune from, and cannot cure, all the ills of the world."

London 2012 marks ten Games since the massacre of the 11 athletes, who were held hostage by Palestinians demanding the release of 234 prisoners in Israeli jails, with the three survivors captured but later released by West Germany following the hijacking of a Lufthansa plane.

Israeli agents, taking part in "Operation Wrath of God", systematically tracked down and killed dozens of people suspected of involvement in the massacre, over the following decade.

One innocent man, a Moroccan waiter in Norway, was also killed.