The likely involvement of a Saudi national in a plot to mail parcel bombs on US-bound planes show Saudi Arabia's battle against Al Qaeda is far from over
Ibrahim Hassan Al Asiri, a 28-year-old who tops Saudi Arabia's terrorism wanted list, has been named by US officials as a key suspect in the plot blamed on the Yemen-based Al Qaeda in the Arabian Peninsula (AQAP).
Believed by Saudi intelligence to be hiding in Yemen, Asiri is one of many Saudi nationals who fled to the kingdom's poorer neighbour after Riyadh began an aggressive campaign against Al Qaeda and its sympathisers at home.
"The Saudis managed to hit Al Qaeda in their home territory but they moved to Yemen," said Abdulghani al-Iryani, a Yemeni analyst in Yemen's capital Sanaa.
"Al Qaeda as an organisation comes from Saudi Arabia. Its funding came from there, and command structure," he said.
Fifteen of the 19 men involved in the September 11, 2001, terror attacks on the United States were from Saudi Arabia and Al Qaeda leader Osama bin Laden was from there, although he had been stripped of his citizenship in the 1990s.
And though the majority of AQAP members are believed to be Yemenis, the group is heavily influenced by Saudis, whose focus is more on launching attacks on Saudi Arabia and abroad rather than on Yemen itself, diplomats and analysts say.
Militants using the Al Qaeda name launched attacks on Saudi Arabia in 2003, and in 2009, Al Qaeda's Yemeni and Saudi wings merged into Al Qaeda in the Arabian Peninsula, which says it wants to topple the Saudi ruling family.
Though the leader of AQAP, Nasser al-Wahayshi, is a Yemeni, the presence of many Saudi fighters in the group poses a particular problem for Saudi Arabia given their family connections in the kingdom and opposition to its rulers.
"Many members are Saudis," said Dubai-based security analyst Theodore Karasik. "Saudis make up many senior positions."
The group's ability to reach right into the heart of the kingdom was demonstrated last year when Asiri's brother blew himself up in a failed attempt to assassinate Saudi Arabia's counter-terrorism chief Prince Mohamed Bin Nayef in Jeddah.
Saudi Arabia brought major operations against Saudi-based Al Qaeda cells to a halt in 2006 after crushing the group with the help of Western counter-terrorism experts.
But it continues to make arrests which indicate that Al Qaeda's appeal among some Saudis remains strong.
In March, Saudi authorities arrested 58 Saudi suspected Al Qaeda militants who had been planning attacks on energy facilities in the world's biggest oil exporter.
"The battle with Al Qaeda is far from over. The fact that so many Saudis were arrested then still shows its appeal," said a Western diplomat in Riyadh.
Saudi Arabia, which provided the intelligence which led to the discovery of the parcel bomb plot, is giving what is believed to be a large amount of financial aid to Yemen to help it fight Al Qaeda in the Arabian Peninsula.
But just as Islamist militants have been impossible to contain as they spread across the Afghanistan and Pakistan border, helped by shared tribal identities and common religious traditions, Saudi Arabia faces a similar problem in Yemen.
Saudi Arabia's Wahhabi tradition, a fundamentalist or "Salafist" form of Sunni Islam which inspires Al Qaeda, has made inroads in Yemen since north and south Yemen united in 1990.
Saudi clerics in the past helped set up Salafist religious schools in Yemen which have become a recruiting ground for militants.
AQAP is able to exploit this shared religious tradition to win supporters among those who regard Saudi Arabia's absolute monarchy as failing to follow their interpretation of Islam.
Diplomats and Saudi journalists also said that Asiri, though raised in Riyadh, was believed to have family roots in the remote Asir province, a poor area near the Yemeni border.
Most of the 15 Saudis involved in the September 11, 2001 attacks came from there.
The southern border areas, part of Yemen in the past, are less developed than the rest of the kingdom and have strong tribal structures, with villages straddling both countries.
"Allegiance here often comes first to tribes not to the country," said one diplomat in Riyadh.
Al Qaeda in the Arabian Peninsula is trying to exploit these tribal allegiances, including by marrying into border tribes, to improve its ability to cross the porous border and plan attacks in Saudi Arabia, diplomats say.
The challenge in defeating Al Qaeda in the Arabian Peninsula is made all the harder by the fact that direct Yemeni government control only extends over parts of the country, leaving other zones to tribal powers.