International security officials are urging countries to make better use of databases on missing travel documents, following revelations that two people used stolen passports to board the missing Malaysia Airlines passenger jet.

Flight MH370 vanished over waters between Malaysia and southern Vietnam early Saturday (March 8th) en route from Kuala Lumpur International Airport (KLIA) to Beijing. While the fate of the Boeing 777-200ER remained a mystery, Malaysia opened a terror investigation after discovering at least two passengers boarded the plane using stolen passports.

In a strongly worded statement, Interpol noted that no one had checked its extensive Stolen and Lost Travel Documents (SLTD) database ahead of the Malaysian flight's take-off.

"Whilst it is too soon to speculate about any connection between these stolen passports and the missing plane, it is clearly of great concern that any passenger was able to board an international flight using a stolen passport listed in Interpol's databases," said Interpol Secretary General Ronald Noble.

"Only a handful of countries worldwide are taking care to make sure that persons possessing stolen passports are not boarding international flights."

In 2013, more than a billion travelers boarded planes without their passports screened against the database, he said. Interpol mentioned the United Kingdom, the United States and the United Arab Emirates (UAE) as three countries routinely using its Stolen and Lost Travel Documents (SLTD).

In a statement Sunday, Malaysian Prime Minister Najib Razak said authorities would review all security protocols, enhancing them "if needed".

"The security in KLIA is already compliant with international standards," Department of Civil Aviation Chief Azharuddin Abdul Rahman told reporters Monday.

The mystery passengers

Austrian Christian Kozel and Italian Luigi Maraldi were on the passenger list, but neither man boarded the plane. Instead, two mystery passengers used their passports, which had been stolen in separate incidents in Thailand.

Flight information seen by AFP shows two tickets in Kozel and Maraldi's names issued in the Thai beach town of Pattaya, south of Bangkok, on March 6th, and paid for in Thai bhat.

Though anyone caught selling or "owning in order to sell" an illegal passport faces a possible 20-year prison sentence, Thailand does not check passports against Interpol's SLTD database, a senior Thai immigration police officer told AFP.

"The key thing is that countries should make it a point to be electronically linked to the Interpol database -- as an added and important layer in the range of border controls to detect false travel documentation used by drug mules or terrorists," said Kumar Ramakrishna, head of the Centre of Excellence for National Security at Singapore's S. Rajaratnam School of International Studies.

Interpol urged countries to screen all passports "for the sake of innocent passengers".

Noble said he hoped the tragedy of flight MH 370 would encourage uniform, worldwide passport screening. "Doing so will indeed take us a step closer to ensuring safer travel," he said.