LONDON — Global politics trumped ceremonial protocol Thursday, as Britain revoked a royal wedding invitation to the Syrian ambassador because of violent government attacks on protesters there.

But critics continued to ask why the guest list had room for despots while former British prime ministers Gordon Brown and Tony Blair, both from the Labour Party, were left out.

Human rights groups had criticized the decision to invite Syrian Ambassador Sami Khiyami to Prince William and Kate Middleton’s nuptials at Westminster Abbey on Friday.

More than 450 people have been killed since mid-March in the uprising against Syrian President Bashar Assad’s authoritarian regime, with 120 dead over the weekend.

The government said ambassadors from all countries with which Britain has “normal diplomatic relations” had been invited to the wedding — some 185 in all — and that an invitation did not condone regimes’ behavior.

But the Foreign Office said Thursday that “in the light of this week’s attacks against civilians by the Syrian security forces, which we have condemned, the foreign secretary has decided that the presence of the Syrian ambassador at the royal wedding would be unacceptable and that he should not attend.”

It said Buckingham Palace shared that view.

Khiyami said he was not surprised by the decision, which he attributed to “the effect of media on government decisions.”

“I find it a bit embarrassing but I don’t consider it a matter that would jeopardize any ongoing relations and discussions with the British government,” he told the BBC.

Britain has been strongly critical of the violence in Syria, and on Wednesday summoned Khiyami to the Foreign Office for a dressing-down.

Other diplomatic omissions from the guest list include the ambassadors of Libya — where Britain is involved in NATO action against Moammar Gadhafi’s regime — and Malawi, whose envoy was expelled from London this week in a tit-for-tat diplomatic feud.

Among the royal wedding invitees criticized by rights activists are Swaziland’s absolute monarch, King Mswati III; the ambassador of President Robert Mugabe’s regime in Zimbabwe; and Prince Mohammed bin Nawaf bin Abdulaziz of Saudi Arabia.

Protesters were planning a demonstration outside Buckingham Palace Thursday to condemn Saudi Arabia’s role in quashing dissent in neighboring Bahrain.

Bahraini Crown Prince Salman bin Hamad Al Khalifa declined a wedding invitation, saying he did not want the Gulf nation’s unrest to tarnish the celebration. Bahrain’s rulers have imposed martial law and are backed by a Saudi-led military force to try to quell an uprising that began in February.

Commentators also noted the omission of Blair and Brown. The two Labour ex-premiers were not invited to the wedding, while their Conservative counterparts John Major and Margaret Thatcher were. Thatcher declined due to poor health.

The palace rejected suggestions the royals felt closer to Conservative politicians than to Labour ones. But some have suggested that Queen Elizabeth II cooled to Blair when he advised the royal family to show more emotion in the wake of Princess Diana’s death in 1997. His wife, Cherie, also reportedly refused to curtsey to the queen and revealed in a memoir that the couple’s son Leo was conceived during a visit to the royal estate at Balmoral.

Palace officials said the decision was not a snub, but a matter or protocol. Brown and Blair are not Knights of the Garter, a ceremonial order of chivalry, while Major and Thatcher are.

Blair insisted he wasn’t offended. During a visit to Colombia, he said the lack of an invitation was “not a problem at all” and wished the prince and his fiancee every happiness, Britain’s Press Association news agency reported.

But former Foreign Secretary Jack Straw said it was odd that Blair and Brown had not been invited while Syria’s ambassador had.

“In retrospect I think the decision-makers probably would have made some different decisions,” he told the BBC.