A major military and intelligence operation is under way in Yemen as authorities attempt to track down an alleged Saudi bomb-maker who is a key suspect in a foiled air cargo bomb plot over the weekend.
The hunt for 28-year-old Ibrahim al-Asiri was launched in the provinces of Maarib and Shabwa on Tuesday, a security official told the Reuters news agency.
"Asiri is believed to be hiding and moving with senior al-Qaeda elements such as Nasser al-Wahayshi [the Yemen al-Qaeda leader]. Security intelligence are still tracking them down to exactly identify their whereabouts," the official said.
Yemen is under immense pressure to find those responsible for planting two explosive devices found in air cargo destined for the US late last week.
Al-Awlaki on trial
In a sign that it is taking tougher measures to crack down on what it sees as radical elements, Yemen put Anwar al-Awlaki, a US-born Islamic cleric on trial in absentia on Tuesday, accusing him and two others of plotting to kill foreigners.
The charges against al-Awlaki came as part of a trial against another man, Hisham Assem, who has been accused of killing a Frenchman in October.
Assem, 19, was present in court, but al-Awlaki and a third suspect, Osman al-Awlaki, were charged in absentia. The hearing was held amid tight security at a courthouse in Sanaa, the capital.
Al-Awlaki, a Yemen-based cleric, has previously been linked by US investigators to an army psychiatrist accused of last year's killings at a base in Frot Hood, Texas.
They also say he helped prepare Umar Farouk Abdulmutallab, a Nigerian accused in the Christmas airline bombing attempt, and that he had links to the failed Times Square bombing.
Governments around the world have tightened security surrounding freight coming from Yemen after two parcel bombs, addressed to synagogues in Chicago, were discovered at a UK airport and in a cargo terminal in Dubai on Friday.
Qatar Airways said the Dubai parcel had been transported on two of its passenger planes from Sanaa via Doha.
Britain banned unaccompanied cargo freight to the UK from Yemen and Somalia, the Netherlands and Canada suspended all cargo flights from Yemen, and France and the US banned air freight from Yemen in response to the plot.
Germany also extended its ban on cargo aircraft from Yemen to include passenger flights, sparking shock from Yemen which described the decision as a "mass punishment".
An official said that such a "rushed and exaggerated reaction to suspicious packages will harm Yemen's efforts in combating terrorism and serves no one but al-Qaeda terrorists who always sought to ... hurt Yemen's interests".
The International Air Transport Association (Iata) has warned against knee-jerk reactions to the incident, saying governments must not make rash moves to improve air security.
"We have seen many cases where [solutions] have unintended consequences," Giovanni Bisignani, director general of the global airlines body said at a meeting in Frankfurt on Tuesday.
"Over the weeks and months, as governments learn more about the threat, we must continue to work together to implement appropriate solutions," he said.
Earlier, US authorities said that they knew that al-Qaeda had planned to use international cargo systems several weeks before last week's foiled plot.
Authorities are reported to have intercepted packages shipped by the group in September.
"Several weeks ago, we identified packages in transit that appeared to have a connection to al-Qaeda," a US official told Al Jazeera on Tuesday.
"We looked at them very closely, and determined they did not contain explosives. We obviously took this earlier event into account in dealing with last week's cargo threat."
The parcel, which was hidden inside a computer printer with a circuit board and mobile phone SIM card attached, was said to contain pentaerythritol trinitrate (PETN), a highly potent explosive, which is difficult to detect in security screenings.
A leading al-Qaeda fighter in Yemen who surrendered to Saudi Arabia last month provided the tip that led to the thwarting of the mail bomb plot, according to Yemeni security officials.
The officials said Jabir al-Fayfi, a Saudi who had joined al-Qaeda in Yemen, had told Saudi officials about the plan.
"The latest announcement about al-Fayfi brings to the fore two major issues," Al Jazeera's Hashem Ahelbarra, reporting from Sanaa, said.
"One, that Saudi Arabia enjoys unlimited influence and leverage in Yemen. Number two, is it shows that Saudi managed to infiltrate al-Qaeda in the Arabian Peninsula.
Ahelbarra said that this was something unheard of in the history of al-Qaeda.
"Usually, when they plan an attack, it is only a small circle of al-Qaeda that is familiar with all the details of the operation," he said.
"The Yemenis don't seem to be happy with the revelations that Saudi was the key player in tipping off the Americans."