The day commemorates the martyrdom of Prophet Mohammad's grandson Hazrat Imam Hussain, killed in the battle of Karbala some 1,400 years ago.
Thousands of Shias staged processions marking Ashura, the 10th day of Shia rituals during Moharram, the first month of the Muslim year.
The day commemorates the martyrdom of Prophet Mohammad's grandson Hazrat Imam Hussain, killed in the battle of Karbala some 1,400 years ago.
The government deployed army and paramilitary forces across the country, determined to curb rising violence between Shia Muslims and the majority Sunni community.
Shia Muslims believe that Imam Hussain is the true leader of Islam following the Prophet's death, but Sunni Muslims disagree.
Bombs found
Police carried out bomb checks using sniffer dogs, streets were cordoned off and hospitals put on standby in an unprecedented show of security.
One man was killed near a procession in the North West Frontier Province but police were uncertain if it was a sectarian attack.
There were no other reports of violence.
Crowds of Shia Muslim men marched through the streets of several cities in the annual ritual of self-flagellation, whipping themselves with blades attached to thin chains.
The AFP news agency reported that police in the southern port city of Karachi recovered a bomb late on Wednesday at a bus stand close to a Shia mosque.
Hours earlier, a bus driver disarmed a device minutes before it was due to explode in his vehicle, police said.
Killings
At least 40 people have died in sectarian violence in the past month and a half.
The killings followed the execution in February of a hardline Sunni activist for the murder of an Iranian diplomat.
Sunni hardliner Haq Nawaz was hanged for the murder of an Iranian diplomat, a Shia Muslim.
Violent clashes followed his execution, which was ordered by a court but was supported by the military government.
More than two dozen people were killed in and around Lahore, the capital of Punjab province, including at least 10 who lost their lives in an armed attack on worshippers in a mosque.
Sectarian killings also took place in Hangu, a town in the North West Frontier Province.
In the days leading up to Moharram, the authorities detained hundreds of activists from hardline Shia and Sunni groups.