A series of attacks in Morocco's largest city Casablanca killed and injured dozens of people - only days after apparently co-ordinated attacks against Western targets in Saudi Arabia.
No group has claimed responsibility but, in the wake of the Riyadh attacks, terror alerts were issued for the United States and countries in Africa, the Middle East and Asia. BBC News Online looks at what is behind the warnings and the latest attack.
What prompted the latest alerts?
In the aftermath of the devastating attack in Saudi Arabia, a flurry of terror alerts went out, underlining fears of a resurgent threat from al-Qaeda.
The warnings - which made no specific mention of Morocco - were largely based on intercepts of communications between alleged plotters.
Among the measures across the world:
- Security has been increased across the United States, with the country's alert status raised to orange - the second-highest level - following renewed threats of attacks
- The US, Britain, Germany and Italy announced the temporary closure to the public of their embassies and consulates in Saudi Arabia amid fears of "imminent" new terrorist attacks
- In Kenya, the authorities said there is intelligence that al-Qaeda members are planning another attack in East Africa; all UK flights to and from Kenya have been cancelled
- The British authorities later issued a warning of a "clear terrorist threat" in six other East African countries - Djibouti, Eritrea, Ethiopia, Somalia, Tanzania and Uganda - and advised travellers to "be on their guard".
- Australia and New Zealand have warned their nationals to be on their guard in South East Asia. The Australian foreign office has told Australians to be extremely cautious in Malaysia, Thailand, Singapore, the Philippines, East Timor and Brunei.
Has the US alert been triggered by specific intelligence?
The BBC security correspondent, Frank Gardner, says there is intelligence emerging from interrogations of suspects held by the Saudi authorities and communications interceptions that is leading the Americans to conclude that there is a heightened risk of an attack in the US, not just on US or Western interest in the Middle East.
US officials have been open and specific about their warnings, suggesting that there is a high risk of suicide or truck bombings, or attacks by armed men.
Was the Casablanca attack the first time North Africa has been hit by violence that might be linked to al-Qaeda?
Although this was the first attack actually on Moroccan soil, al-Qaeda are thought to have been active there before.
Last year, a major plot was uncovered, with the help of Western and Arab intelligence, to attack US and UK warships in the Strait of Gibraltar. Three Saudis were jailed for 10 years for what a Moroccan court decided was an al-Qaeda plot.
Also, the bombing of a synagogue on the Tunisian resort island of Djerba in April 2002 - which left some 20 people dead - is widely believed to have been the work of al-Qaeda operatives.
Are these kinds of alerts reliable?
Warnings of imminent terrorist attack seem to have come thick and fast over recent years. It is almost impossible to decide on the seriousness or urgency of an individual alert.
Security officials often issue the alerts based on intelligence picked up by their security agencies. The intelligence can come from a wide variety of sources. Alerts are often triggered by communications intercepts. Some alerts have been issued on the basis of interrogations at Guantanamo Bay.
Often alerts and the security measures that follow them actually appear to prevent an attack by sending the potential attackers into hiding.
In the case of the attacks in Riyadh, there was clear intelligence that an attack was imminent, but Saudi security agencies failed to pinpoint and prevent the attacks.
How powerful and active is al-Qaeda?
There can be little doubt that al-Qaeda is still active despite more than 18 months of the "war on terror". It seems to have reorganised itself to compensate for the destruction of its bases, the capture of some of its top leaders and a crack down on its financial operation.
In a recent report, the International Institute of Strategic Studies warned that Osama Bin Laden's organisation is today "more insidious [than] and just as dangerous" as it was in the run-up to 11 September.
However, there is a problem of definitions. Are attacks like those in Riyadh and Mombasa in any way planned, financed or organised by Bin Laden or the organisation he is still believed to lead? Or are these attacks carried out by groups that may have no connection to al-Qaeda other than sharing its aims, ideals and methods?