Afghanistan: 'Sectarian' twin attacks kill 52
Twin attacks apparently targeting Shia Muslims have killed at least 52 people in Afghanistan.
In the deadliest incident, a suspected suicide bomb struck a shrine packed with worshippers in the capital, Kabul, killing at least 48.
Another blast hit the northern city of Mazar-i-Sharif at about the same time, killing four people.
The attacks appear to be of a sectarian nature unprecedented in recent Afghan history, correspondents say.
They coincided with the Shia Muslim festival of Ashura - the most important day in the Shia calendar and marked with a public holiday in Afghanistan.
Ashura is the climax of Muharram, the month of mourning for the martyrdom of the Prophet Muhammad's grandson.
Though tensions exist between Afghanistan's Sunni and minority Shia Muslims, most attacks in Afghanistan in recent years have targeted government officials or international forces, correspondents say.
The near-simultaneous explosions happened at about midday (07:30 GMT).
In Kabul, the bomb went off near a gathering of hundreds of Shias singing at the Abu Fazal shrine, AFP news agency reported.
Senior police and health ministry officials said 48 people were killed in the blast.
"I was there watching people mourning [for Ashura] when there was suddenly a huge explosion," witness Ahmad Fawad told AFP.
"Some people around me fell down injured. I wasn't hurt, so I got up and started running. It was horrible," he said.
Amid the chaos straight after the blast, a young girl, dressed in a green shalwar kameez (traditional dress) smeared in blood, stood shrieking, surrounded by the crumpled, piled-up bodies of children, AFP reported.
Afghan President Hamid Karzai spoke of the unprecedented nature of the attack, saying it was "the first time that, on such an important religious day in Afghanistan, terrorism of that horrible nature is taking place".
The blasts also caused scores of injuries, with sources at the Afghan health ministry saying 67 casualties have arrived at hospitals.
Police said they foiled another attack elsewhere in the capital.
The bomb which exploded near the main mosque in Mazar-i-Sharif was apparently strapped to a bicycle, and went off shortly after the Kabul blast.
Balkh province Deputy Police Chief Abdul Raouf Taj said the device exploded as a convoy of Shias, shouting in celebration of Ashura, passed by, the Associated Press news agency reported.
Elsewhere, police said at least three people were wounded by a motorcycle bomb in the southern city of Kandahar, the Taliban's heartland - but it appears to be unconnected to the other two attacks.
There are tensions between Sunni and minority Shia Muslims in Afghanistan, but violence of the type seen in Pakistan or Iraq is rare, the BBC's Quentin Sommerville in Kabul says.
Over the past decade Shias in Afghanistan have celebrated their festivals more confidently, openly and on a bigger scale than ever before.
The attacks come a day after an international conference on Afghanistan's future was held, in the German city of Bonn.
Pakistan boycotted the conference, after a Nato attack killed 24 of its troops at a checkpoint near the Afghan border last month.
Afghan security officials held their breath during the conference, our correspondent says, fearing there might an attack in Kabul to divert attention.