A three-day curfew was imposed  in Rawalpindi city, after eleven people were killed  and a market was burnt, following a clash reportedly between Sunni and Shia  crowds on Ashura , the 10th day of the Islamic month Muharram, a day of mourning and processions  for Shia-muslims.
Soon after the clash on November 15, 2013, images – some doctored and some manipulated with propaganda  – quickly spread on social media, putting the blame for the violence on either Sunnis or Shias. Just a day after the Rawalpindi unrest, rare spates of violence broke out  between Shia and Sunni crowds in different parts of the country, which the Pakistani government has blamed on the negative role played by “social media”  during the Rawalpindi clashes.
On 22 November, twin bombings killed nine people and injured 28 others  in a Shia-dominated neighborhood of Karachi. The banned militant group Tehrik-e-Taliban Pakistan (TTP)  claimed responsibility for the attack, saying the bombings were revenge for the Rawalpindi incident. 
Journalist, anchor and blogger Mansoor Ali Khan (@MansoorGeoNews ) tweeted a picture of his colleague who was killed in the Karachi bombings:
— Mansoor Ali Khan (@MansoorGeoNews) November 22, 2013 
According to reports, the situation turned violent in Rawalpindi, a garrison city that borders capital Islamabad, on November 15, after a cleric made inflammatory statements on a loud speaker at a Deobandi mosque along the path of an Ashura procession in a popular market area, agitating and offending both Shias and Sunnis. The cleric denigrated the Prophet Mohammad's grandson, a revered figure across all sects of Islam, whose death Shias mourn on Ashura. Blogger Sarah Khan wrote about the account of an eye-witness on the Let Us Build Pakistan (LUBP)  blog:
According to the eye-witness, Mullah’s inflammatory speech agitated the mourners in procession. [..] Agitated (Shia and Sunni) mourners finding it difficult to bear the (Deobandi) mullah (cleric) started shaking the grills outside the mosque in protest against the comments. In meantime someone from inside mosque 1st hurled a stone at mourners shaking the grills. The stone was followed by firing from mosque rooftop. Firing caused panic and people started running. [sic]
The situation deteriorated when people exchanged gunfire and dozens of shops around the mosque were torched. Once the police failed to get a hand of the situation, the army imposed a curfew, and invoked “Section 144,” which prohibits groups of five or more people from assembling. The curfew was lifted on 18 November , several culprits have been identified through security footage and a judicial inquiry  into the clashes is underway, but the overall mood in Pakistan is tense.
Rare sectarian clashes
While Shia mosques and Ashura processions have been been targeted and attacked by banned anti-Shia militant groups in Pakistan, the Rawalpindi incident marked a rare spontaneous clash between Sunni and Shia crowds.
Just a day after the Rawalpindi unrest, isolated incidents of violence broke out  between Shia and Sunni groups in various parts of the country. Hundreds of miles south of Rawalpindi, several people were injured in Multan city and a group damaged a Shia mosque and shops  in the neighbouring town of Chishtian.
A hundred miles north-west of Rawalpindi, violent clashes in Kohat, also linked to the Rawalpindi incident, took the lives of three people; officials imposed a curfew there. On November 19, a hundred miles east of Rawalpindi, a Shia senior official of the University of Gujrat, Syed Shabbir Hussain Shah , was gunned down, and his killing is also being investigated for links to the Rawalpindi unrest.
Role of social media
While all this was happening, Prime Minister Nawaz Sharif was on official visits to Sri Lanka and Thailand for which his newly elected government is being criticized . Nawaz Sharif in turn accused social media  for playing a ‘negative role’ during the clashes.
A former Pakistani policeman writes about the failure of police to use social media to its advantage to control the aftermath of the Rawalpindi i ncident in the daily Dawn:
To reinforce their influence, extremist groups increasingly rely on social media but our law enforcement and regulatory agencies still don’t know how to tackle the challenge. Social media can be effectively used to bring the police and community on one page. In mega urban centres, apart from the physical presence of the law enforcers, people expect the online presence of the police. [..] Police need to learn quickly about social media to keep pace. Many police forces around the world have started to use it for engagement, intelligence and investigation, and often release pictures or videos of wanted criminal and terrorist suspects on their websites.
The websites of police departments in Pakistan, on the contrary, are neither public friendly nor interactive. This is a pity as police websites could help in the introduction of e-policing in urban areas.”
Rawalpindi native Qurat-ul-Ain Fatima  writes in her blog during the curfew which ended on November 19:
As army roams around the streets of the city trying to “keep peace” , the social Media buffs are making their own statements book justifying this or that picture as the proof of perpetrator to be “Shia” or “Sunni”. The Humanitarian aspect of the tragic event and its long lasting repercussions have almost escaped everyone’s thought. The trend shows we will forget the incident as soon as the temporary peace is restored. [all sic]
Sectarian violence in Pakistan
In recent years, sectarian extremists and militant groups  with links to the Taliban and AlQaeda have routinely targeted Shias, followers of liberal strands of Sunni Islam (Barelvis) and other religious minorities in the country, namely Christians and Ahmadis. A church bombing in Peshawar on September 22, killed over 80 Christian worshippers. 
Banned anti-Shia militant groups Lashkar-e-Jhangvi , Lashkar-e-Taiba /Jamaat-ud-Dawa , Sipah-e-Sahaba Pakistan  (SSP) and Ahle-Sunnat Wal Jamaat  (AWSJ) have claimed responsibility for many bombings. According to a former Interior Minister of Pakistan, Lashkar-e-Jhangvi is believed to be behind 80 percent  of terrorist attacks in the country.
Peace-loving sunni Muslims of #Pakistan  should immediately distance themselves away from banned outfits ssp/aswj if they already have not.
— Shahbaz Zahid (@shahbazzahid) November 17, 2013 
Anti-Shia groups have left the Hazara community  in Balochistan , in Southwestern Pakistan, in a helpless situation. They refused to bury their loved ones after twin-bombings, which Lashkar-e-Jhangvi claimed responsibility for killed dozens from their Shia -Hazara community earlier this year.
In the lead up to Muharram and Ashura, Pakistan's leading newspaper Dawn published the editorial Tensions High: Muharram Security :
The sectarian militants are well organised and have their own system of gathering information. They have access to the latest technology and are a step ahead of the overall counterterrorism strategy. That is where we can see the gap. The political face of sectarianism is known to the intelligence agencies; but greater efforts are needed to crack down on militants. Without a serious approach to the problem of sectarian militancy, the risk of communal flare-ups, which has so far not manifested itself in most places, cannot be discounted […] At the same time, a check is also required to be kept on those who show their hate towards communities through incendiary speeches and literature. Engaging rational-minded Shia and Sunni religious scholars would be indispensable to this exercise.