Nearly 100 people were killed and at least 200 injured when a suicide blast  targeted a military parade rehearsal in Yemen's capital Sana'a on May 21.
The bomber, dressed in military uniform, detonated his explosives in the middle of soldiers rehearsing for a parade to mark the 22nd anniversary of the unification  of North and South Yemen.
Al Qaeda (AQAP ) have apparently claimed responsibility  for the attack, in revenge for what it described as the US war  against it in southern Yemen. However, many Yemenis have expressed their doubts.
The following video  [ar] shows the immediate aftermath of the explosion on Sabaeen Street in Sana'a [WARNING: DISTRESSING IMAGES].
Journalist Tom Finn was at the scene:
@tomfinn2 : In Sabaeen. Police everywhere, pieces of flesh scattered over the tarmac. Injured all in hospital. #yemen
@tomfinn2 : Ambulances still racing around Sana'a. Doctors say hospitals are overwhelmed. #Yemen
Farea Al Muslimi, a student activist based in Beirut, commented:
@almuslimi : This is a terrifying day in #Yemen and at the same time golden chance for [President Abdou Rabbo Mansour] #Hadi to take urgent strong measures in restructuring the army.
President Hadi indeed issued a decree  [ar] after the attack replacing top security officials, including a nephew of former president Ali Adullah Saleh.
Mai Saleh tweeted:
@A4Mai : Fadhel AlQawsi is appointed as the new commander of the Central Security forces by decree of President #Hadi #Yemen
@A4Mai : So Ammar [Saleh's nephew] is out? Did we have to witness a disaster for these decrees to come? #Yemen
Although some news sources have stated that Al Qaeda has claimed responsibility for the attack, many are waiting to learn more.
Yemen scholar Gregory D. Johnsen commented:
@gregorydjohnsen:  Less rumor mongering please about today's attack in #Yemen. I promise it is ok to say: “I don't know”
And demanding more evidence, Mai Saleh tweeted:
@A4Mai:  Would love to see that #AQAP statement in which it claimed responsibility for the attack #Yemen
News of Yemen Revolution  Facebook page posted that 12 hours prior to the explosion, a pro-Saleh page on FB predicted the explosion and provided a link, which was subsequently removed.
Mohammed wondered how the suicide bomber went unnoticed:
@Yemen4Change : #Yemen | the word is: the suicide bomber was wearing military clothes & a belt packed with explosives, NO ONE NOTICED? #Sanaa
While Farea Al Muslimi asked:
@almuslimi : Why didn't #Saudi help by intelligence info about #AQAP as it did regarding the bombs being sent to #US? #Justwondering #YEMEN
Amid the many speculations and question marks, Yemen's Human Rights Minister Hooria Mashhour tweeted:
@Hooria_Mashhour : Transparent investigation should be done for all these mass crimes against humanity #yemen
Ataf Alwazir, a prominent Yemeni activist and blogger, encouraged people to look deeper than the repetitive news circulating:
@WomanfromYemen : always keep an open mind & dont take everything as it is. Dont be a copy paste person. Question & analyze. Thats why we have a mind.
The day of the blast was certainly one of the saddest days Sana'a and Yemen have ever seen. The attack raises questions regarding the efficacy of the joint US-Yemeni counterterrorism strategy, and give credence to the argument  that US drone strikes are counterproductive and simply fuel extremism.