Officials in Pakistan say the death toll has reached at least 43 in Tuesday's attack on a Shi'ite religious procession. The dead include six police officers reported to have been killed in the crossfire.
Officials in the southwestern Pakistani city of Quetta say Tuesday's attack was carried out by three men, who fired into a large crowd of Shi'ite worshipers before detonating explosives strapped to their bodies.
They say one of the assailants survived and is now in custody.
Witnesses say shots were fired at the religious procession from a nearby building, indicating other attackers were also involved.
Local Provincial Chief Minister Jam Yousef told reporters the attackers were likely militants who came from outside Quetta, and that several police officers are also being questioned in connection with the incident.
Foreign Office spokesman Masood Khan told reporters an investigation is under way.
"There is no doubt in our mind, that there is an evil mind behind these attacks. … We shall repulse all these dark designs against the state and people of Pakistan," he said.
The attack took place at the height of the Muharram holiday period, an occasion of special religious importance for Shi'ite Muslims.
Sectarian violence between extremists from Pakistan's majority Sunni Muslims and the minority Shi'ites has long plagued the country.
But Pakistani political commentator Ayaz Amir says this and other recent incidents of Sunni-Shi'ite fighting is more likely aimed at the government than rival religious sects.
"Sectarianism is the form that it is taking - I mean, those are the targets. But I think the aim is the government, trying to destabilize it, trying to create a general unrest," he said.
Late last year, Pakistan began cracking down on militant movements in the country, many of which are opposed to the government's cooperation with the United States in its efforts against global terrorism.