Security officials say a leading al-Qaida militant who had surrendered to Saudi authorities supplied the tip that foiled a plot to mail bombs to U.S. destinations.
Yemeni, Saudi and British officials said on Monday that former Guantanamo Bay detainee Jabr al-Fayfi rejoined al-Qaida in Yemen before turning himself in to Saudi authorities and providing the intelligence.
German officials said Monday two parcels intercepted last week that were addressed to synagogues in Chicago contained enough explosives to cause "significant damage." They say one package held 400 grams of the explosive PETN, while the other had 300 grams of the substance.
The United States has sent a team of experts to Yemen to help screen U.S.-bound air cargo following the plot.
U.S. Transportation Security Administration (TSA) chief John Pistole told the CBS Early Show Monday that the U.S. is working with its international partners to increase defenses against a "determined enemy."
He said the TSA team in Yemen will provide training, equipment and expertise to examine cargo shipments at Sana'a airport.
Yemen's aviation authority says it is tightening security at all of its airports.
Despite the increased precaution, Germany has extended its ban on air freight from Yemen. Britain has suspended all air cargo from Yemen and Somalia.
Yemeni authorities are searching for the suspected bomb-maker, whom U.S. officials have identified as Ibrahim Hasan al-Asiri of al-Qaida's Yemen branch.
Al-Asiri also is suspected of making the bomb that attempted to blow up Saudi Arabia's deputy interior minister, Prince Mohammed ben Naif, in 2009.
The Obama administration's counter-terrorism advisor, John Brennan, says forensic analysis indicates the bomb-maker in this plot also made the devices involved in the failed bombing of a Detroit-bound airliner last December (25, Christmas Day).
Brennan said American investigators now are taking a closer look at the crash of a UPS cargo plane in Dubai in September. But investigators from the United Arab Emirates said Sunday there is no evidence the cargo plane was brought down by an explosion.
Yemeni officials said they have released a woman who was held on suspicion of having sent the parcel bombs on U.S.-bound flights.
The young woman, engineering student Hanan al-Samawi, was detained Saturday together with her mother after being tracked down through a mobile phone number on a receipt at the cargo company. It is not clear why the Yemeni authorities have released her.
Students rallied in front of Sana'a University Monday in support of the young woman.
Some information for this report was provided by AP and AFP.