China is joining other countries across the world in tightening air security measures after a series of parcel bomb plots were reported over the past week.

?This file photo shows a police dog inspecting parcels at Guangzhou Customs on March 9. [Fan Yong / China News Service]

The International Air Transport Association on Tuesday called on security regulators around the world to work together to make the skies more secure by addressing the challenges related to cargo security and data collection.

The association urged governments and industry on Tuesday to rapidly develop effective equipment such as oversized X-ray machines to screen the cargo containers that carry most airborne freight.

A source close to the Civil Aviation Administration of China told China Daily on Tuesday that the country's aviation security departments have also "adjusted their strategies" after the reported parcel bomb attempts, but declined to give more details on their measures.

The move came in light of last week's interception of US-bound parcel bombs sent from Yemen.

Parcel bombs exploded at the Swiss and Russian embassies in Athens on Tuesday, following an explosion at a delivery service on Monday that injured one worker. Numerous other bomb attacks were foiled in Greece in the last couple of days, though no link has been made to the Yemen case.

Sources with the Beijing Capital International Airport and the city's postal system said the security measures focusing on mail and parcels have been tightened over the past two days.

A staff member surnamed Zhang with the Beijing Capital International Airport's aviation security company said that they have strengthened safety checks on international freight and mail, especially those sent to the United States.

"Every posted parcel will go through an X-ray scanning device. We pay particular attention to packages containing lumps or powder, which will go through explosive testing and be opened for inspection if necessary," he told China Daily.

Packages containing electric equipment and organic materials will have to pass explosive testing and be opened for inspection, he said. Those without complete addresses will be sent back, he added.

The capital's postal system has also paid attention to the warning, as Li Ming, who is in charge of parcel logistics at the Beijing-based East District Post Office under the Beijing Post Company, said international mail and parcels will be checked three times before being sent out.

Every parcel will first be checked at the post office in front of the sender. Packages will be double-checked at a sorting center and then checked by the Customs a third time, he said.

But anti-terrorism experts warned there are loopholes in the country's aviation security.

Li Wei, an anti-terrorism expert at the China Institutes of Contemporary International Relations, said security checks on passenger flights are much stricter than on cargo flights.

After passing the first security checkup at the airport, air mail and parcels will not be subject to more security checks even when they are loaded onto a transfer flight, because "airlines and airports tend to believe more checks will be a waste of manpower and resources", he said.

As countries have different security measures, the lack of double-checks will give terrorists the chance to use loopholes and send mail bombs through the weakest link, he said.

"The foiled parcel bomb plots brought warnings to China, especially the cities holding big events, such as Guangzhou where the Asian Games will open soon," he said.

Relevant departments must attach importance to the logistics check, especially on airmail and parcels, he warned.