British Foreign Secretary Philip Hammond speaks at the American Enterprise Institute in Washington on Tuesday. (Jim Watson/AFP/Getty Images)

Incompetent or complicit Egyptian security was probably involved in the Oct. 31 crash of a Russian passenger jet in Egypt’s Sinai Peninsula, British Foreign Secretary Philip Hammond suggested Tuesday, saying that his government’s belief that a bomb was placed aboard the plane had “hardened” over the past week.

“We are acutely aware” that terrorists throughout Europe have the capability and intent to place explosives aboard a civilian airliner, Hammond said, “but they haven’t been able to do it” because of strong security restrictions.

“Where this points the finger is at the capability of the security on the ground at Sharm el-Sheikh,” the Sinai seaside resort where the airliner carrying mostly Russian tourists took off, he said. All 224 people aboard were killed when the plane, bound for St. Petersburg, disintegrated in the air shortly after takeoff.

Many countries around the world have “the idea that security is about buying some new machines and writing up a manual,” Hammond said. “That’s the key cultural challenge which we’ve got to overcome, not just in Egypt but in many systems that will have to look again at the way the people who are doing this security are managed, overseen, incentivized . . . vetted, trained and selected.”

Suggestions last week by both British Prime Minister David Cameron and President Obama that the plane possibly was downed by a bomb were initially dismissed by Russia as speculation.

But Russia has since joined Britain in suspending all flights to Egypt, a ban that a senior Russian official said Tuesday would last for “several months at the minimum.” The two countries are among those sending the most tourists to Egypt; both have dispatched special planes to retrieve tens of thousands of their nationals stranded in Sharm el-Sheikh.

“It is not possible to cardinally change the system of safety, security and checks in a week or even a month,” Sergei Ivanov, the Kremlin’s chief of staff, told journalists in Helsinki following a meeting with the Finnish president.

Egypt, whose tourism industry is reeling from the crash, has said an investigation is ongoing and has cautioned against speculation as to the cause of the crash. Egypt and Russia, along with France, where the maker of the Airbus A321-200 that went down is headquartered, are participating in the investigation but have released no information as to their initial findings.

Hammond, speaking with journalists in Washington, said the fact that the Russians decided to evacuate their nationals and suspend flights, along with the fact that “they are in possession of the key forensics . . . reinforces our sense that it is more likely than not to have been a bomb.”

“I don’t really think there’s anybody left around who doesn’t recognize that this is more than likely a bomb,” he said.

The Islamic State affiliate in the Sinai has at least twice asserted that it brought down the plane, although there has been no confirmation of whether this is true.

Speculating as to the involvement of the Islamic State, also known as ISIL, Hammond said that “there are three tiers” of possibility. “There’s ‘ISIL central’ in Raqqa,” the north-central Syrian city considered the militants’ de facto capital, “and this could have been a centrally directed plot, planned and directed from Raqqa,” he said. “It’s not likely, but it’s possible.”

“It could have been something that ISIL Sinai, a franchise operation, has put together itself and implemented. Or it could have been a lone-wolf operation” by “self-radicalized” individuals influenced by Islamic State propaganda, he said.

Even as Egypt and Russia were saying last week that the crash could have been caused by structural defects in the plane, Hammond recalled, “we had to make a decision because we had aircraft on the ground waiting to take off” and were receiving “information, some of which is open-source, some of which is intelligence-based, which was pointing more and more clearly to the possibility that this could have been an explosive device.”

On Wednesday afternoon, Britain decided to suspend its flights. Hammond said the government “sent a bunch of experts out to Sharm el-Sheikh overnight . . . [and] got a report back from them at 7 a.m. Thursday morning and, frankly, on the basis of what they were seeing” on video surveillance of the search area where the plane crashed and security over the previous several days, “decided that we had to stop flying until the Egyptians had sorted it out.”

Asked whether Egypt was likely to resist expensive and intrusive new security, Hammond said that “they have a choice. If they don’t want our tourists spending hundreds of millions of dollars, they have that option.”

“But it’s clear that we will not allow our airlines to fly into airports that we don’t think are safe. And the onus is on local authorities to put into place the measures that we require,” he said. Tourism composes up to 6 percent of Egypt’s gross domestic product, Hammond said, and “they really can’t afford not to step up to the challenge here.”

Now that the Russians have also pulled out of Sharm el-Sheikh, “there’s nowhere for [the Egyptians] to go,” he said. “They can’t claim this to be some weird British obsession. The Russians have drawn the same conclusion that we have.”

Missy Ryan in Washington and Andrew Roth in Moscow contributed to this report.