PARIS — Interpol knew about stolen passports that two passengers used to board an ill-fated Malaysia Airlines flight bound for China, but no authorities checked the police agency’s vast database on stolen documents beforehand, it said Sunday — baring a gaping loophole in global cooperation against one of the world’s biggest but most unrecognized security threats today.

It’s not known whether stolen passports had anything to do with Saturday’s disappearance of the Boeing 777 bound from Kuala Lumpur, Malaysia, to Beijing with 239 people on board. But such oversights aren’t new — and the case points to a little-known threat to security and Interpol hopes national authorities will “learn from the tragedy.”

More than 1 billion times last year, travelers boarded planes without their passports being checked against Interpol’s database of 40 million stolen or lost travel documents, according to the Lyon-based international organization.

Interpol has made warning about the issue for years, and just last month it bemoaned that “only a handful of countries” regularly use its stolen or lost travel documents database of records from 167 countries. For example, the database was searched more than 800 million times last year — but one in eight searches was conducted by United Arab Emirates alone.

On Sunday, Interpol Secretary General Ronald Noble said in a statement that his organization has long asked why countries would “wait for a tragedy to put prudent security measures in place at borders and boarding gates.”

“Now, we have a real case where the world is speculating whether the stolen passport holders were terrorists, while Interpol is asking why only a handful of countries worldwide are taking care to make sure that persons possessing stolen passports are not boarding international flights,” he said.

Noble, who has called passport fraud one of the world’s greatest threats, said he hopes “that governments and airlines worldwide will learn from the tragedy of missing flight MH 370 and begin to screen all passengers’ passports prior to allowing them to board flights.”

The declared thefts of the two passports used — one of Austrian national Christian Kozel in 2012, and one of Luigi Maraldi of Italy last year — were entered into Interpol’s database after they were stolen in Thailand, the police body said.

Interpol also said it and national investigators were examining other suspicious passports and working to determine the true identities of those who used the stolen passports to board the Malaysia Airlines flight.

In November, in yet another talk on the subject, Noble said that four of every 10 international passengers are still not screened against the Interpol database, which produced more than 60,000 hits in 2012.

Some countries have taken the threat more seriously than others. In 2006, U.S. authorities scanned the Interpol database about 2,000 times — but did so 78 million times just three years later.

Interpol, which has 190 member countries, says rising international travel is creating a new market for identity theft, and bogus passports have found a market among many people: Illegal immigrants, terrorists, drug runners — pretty much anyone looking to travel unnoticed.

Sometimes, authorities are outmatched: Ticket-buying regulations and border control techniques vary from country to country, and an Interpol official says there’s no one-size-fits-all explanation why some countries don’t use its database systematically. The U.S, U.K. and the United Arab Emirates are the biggest users, Interpol says.

In Thailand, where immigration police last year caught a Thai man with 5,000 fake passports, officials say international cooperation helps battle the plague — but passport forgers are now using advanced technology.

“It must take great skills and expertise by our officers to detect the fake passports and visa stamps because the system cannot detect them the whole time,” said Maj. Gen. Warawuth Thaweechaikarn, commander of the Immigration Police’s investigative division. Thai authorities also say some new techniques include finding a lookalike to match the passport, or altering the image on the passport to look like the holder.

Interpol is now reaching out to the private sector. It’s preparing an initiative called “I-Checkit” that will let businesspeople in the travel, banking, and hospitality industries screen documents against the lost-documents database when customers book a flight, check into a hotel room or open a financial account. The project is still being worked out, an official said.

With untold millions of state-issued passports in use worldwide, citizens can help with vigilance.

Police Lt. Gen. Panya Maman, told reporters that Maraldi, the 37-year-old Italian, had deposited his passport as a guarantee at a motorbike rental shop. But when he returned the bike, the shop said they’d already given his passport to some guy who looked like him. Maraldi then filed a missing passport report to local police in Phuket in July.

Speaking Sunday in Bangkok, Maraldi said he had no idea who made off with it.