Yemen's terror haven

German officials had planned to reopen the country's embassy in the Yemeni capital, Sanaa, earlier this week, but later announced the doors of the German outpost will remain closed indefinitely.

"This is our own assessment, which we have taken against the backdrop of the American assessment," Andreas Peschke, a spokesperson for the German Foreign Ministry, told Deutsche Welle.

The United States this week had temporarily closed 22 embassies and consulates from North Africa to South Asia as a reaction to the suspected terror threats. The situation in Yemen is considered to be especially dangerous and the United States and Great Britain have already flown out their diplomatic staff and have urged their citizens to do the same. The Netherlands also pulled all diplomatic staff from Yemen, the country's foreign minister said.

According to reports by The New York Times, the terror warning by the US is based on intercepted messages between al Qaeda leader Ayman al-Zawahri, and the head of al Qaeda in the Arabian Peninsula (AQAP), Nasser al-Wahishi. Michael McCaul, chairman of the US House Committee on Homeland Security, called the threat of attacks "probably one of the most specific and credible threats I've seen since 9/11."

Al Qaeda active in Yemen for the last two years

Al Qaeda has been active in Yemen before the Arab uprising that began in 2011. However, the terrorist organization increasingly used the country as a safe haven amidst the chaos after the revolutions started. Yemen is the poorest of all Arab countries. Almost half of the 23 million Yemenis make due with less than two U.S. dollars per day. Nearly 30 percent of the population is unemployed.

"Yemen is thus the ideal territory for al Qaeda," said Günter Meyer of the Center for Research on the Arab World in Mainz, Germany.

According to Meyer, there are many inaccessible areas in Yemen where suspected terrorists could hide. In addition, the provisional government led by Abed Rabbo Mansur has lost control over vast expanses of the country. In the North, Houthi rebels have been fighting with government troops for years. In the formerly communist South, separatists are fighting for independence from the rest of Yemen.

Al Qaeda began exploiting the chaotic situation about two years ago, particularly in southern Yemen, to extend their sphere of influence. "There was a huge al Qaeda offensive there," said Meyer. However, US drone attacks were able to push back the terrorist group from some southern areas.

Al-Wahishi: the man behind the attacks

The terrorist group had to face some territorial losses. However, "they have managed to militarily organize themselves exceptionally well with the help of Nasser al-Wahishi, who has been described as a charismatic jihadist," said Meyer. He added that AQAP owes it to this man that they are still perceived as the most dangerous branch of al Qaeda.

Al-Wahishi was previously Osama bin Laden's private secretary in Afghanistan. He fled to Iran in 2001 but was turned over to Yemen in 2003 and arrested there. Al-Wahishi then fled from a prison during a mass jailbreak and thanks to his close relationship with bin Laden, was quickly assigned a leading role within the AQAP, which emerged from an amalgamation of Yemeni and Saudi Arabian al Qaeda groups.

In the following years, Yemen's terrorists became better known in the wake of several attacks. In late 2009, the Nigerian "underwear-bomber" Omar Faruk Abdulmutallab attempted to blow himself up on a transatlantic flight with an explosive charge hidden in his underwear. He was trained and equipped in Yemen. In November 2010, the group took responsibility for the placement of a parcel bomb in a UPS cargo plane, which had crashed two months earlier.

Timing attacks to an anniversary?

"Arms deliveries, which come via East Africa, have ensured that the terrorists in Yemen are well equipped," said Meyer.

Al Qaeda head al-Zawahri, who has apparently lived underground in Pakistan for years, has named the Yemeni Al-Wahishi as the second most important man of al Qaeda - making him the head planner of attacks against the West. Meyer further explained that al-Zawahri will keep his leading position, but al-Wahishi will now be responsible for the local plots.

According to information given to Philipp Mißfelder, the foreign-policy spokesperson for German Chancellor Angela Merkel's Christian Democratic Union, experts believe a power struggle has emerged within al Qaeda regarding who will execute the next big attack against the West.

Experts also speculated about the timing of such an attack. It could happen in the coming weeks to mark the first anniversary of the attack against the US embassy in Benghazi, which killed the US ambassador to Libya, Chris Stevens, on September 12.