Pakistan bomb: Karachi standstill after Shias attacked
The Pakistani city of Karachi is in mourning after a powerful bomb ripped through a mainly Shia Muslim area, killing at least 45 people.
Schools and businesses are closed after a strike was called to protest against the attack in Abbas Town.
No group has yet said it planted the bomb, which went off near a mosque as worshippers left evening prayers.
Pakistan's Shia minority are the target of frequent sectarian attacks from Sunni militant groups.
Sunday night's explosion destroyed several buildings and set others on fire, sending a huge column of smoke into the sky and causing a power cut in part of the city.
Police are investigating whether it was a suicide attack and some reports have spoken of a second explosion.
At least 150 people were wounded by the blast, police say.
Monday's strike, being observed in several cities across Sindh province, was called by an alliance of political groups.
Public transport stayed off the roads and petrol pumps and filling stations were also closed. Three days of mourning have also been announced by Shia groups.
Some relatives and local residents were still sorting through the rubble on Monday morning.
"I am here to look for my relative,'' Farzana Azfar told the Associated Press news agency. "People say he was here. But people say they have no idea about him. It appears that some bodies are still in the rubble," she said.
Pakistan's main political and religious leaders rushed to condemn the attack - the latest to target the Shia minority.
But the ability of the authorities to protect Shias is being severely tested, correspondents say - and this as elections are around the corner.
Some activists called 2012 the worst year in living memory for attacks on Pakistan's Shia community, with rights groups estimating that about 400 perished in militant attacks.
But this year is also shaping up to be among the deadliest: nearly 200 people were killed in two separate bombings targeting Shias in the south-western city of Quetta in January and February.
Although no group has yet said it carried out this latest bombing, suspicion is likely to fall on Sunni militant groups.
Groups such as Lashkar-e-Jhangvi have long regarded Shia Muslims as heretics and have stepped up attacks in recent years.
They are thought to have set up several training camps for militants, and police seizures have shown they have access to large quantities of weapons and explosives, the BBC's M Ilyas Khan in Islamabad says.
Last month Pakistan's Supreme Court called on the authorities to devise a strategy to protect Shia Muslims more effectively, given the increase in attacks.
Karachi - Pakistan's biggest city and commercial capital - has a long history of violence.
As well as a sectarian divide between Sunni and Shia, that city has also seen conflict between different ethnic communities - Pashtuns from north-west Pakistan, Mohajirs (immigrants from India following the Partition in 1947) and Sindhis.