Shia and Sunni Muslims in Pakistan have exchanged fire killing at least four people in and around the north-western town of Hangu, say officials.
Much of Hangu's bazaar was destroyed in subsequent rioting
On Thursday a suspected suicide bomber attacked a Shia procession in Hangu. More than 30 people died in the blast and subsequent rioting.
Shia and Sunni leaders have been appealing for calm.
But the BBC's correspondent in Hangu, Haroon Rashid, said tension remained high in the town on Friday.
He said police in Hangu, in North-West Frontier Province, had not yet got the situation under control.
Both groups are armed with both heavy and light weapons and about 70% of shops in the market area have been burned down, he reports.
Police and Frontier Corps personnel were patrolling the market area, which remained under an indefinite curfew.
No one has claimed responsibility for Thursday's bomb which happened as hundreds of Shias were marking Ashura, the holiest day in the Shia calendar.
Pakistan has a history of Shia-Sunni tension and security is tight across the rest of the country to prevent any of the violence from spreading.
The mayor of Hangu, Ghaniur Rehman, said two people were killed on Friday in Hangu and two more in the nearby village of Ibrahimzai.
Maulana Khurshid Anwar, a leader of the Shia procession, said Thursday's explosion happened just as he was about to address the crowd.
There were several reports of gunfire, with officials saying that four of the dead were killed in a gun attack on a minibus.
A judicial inquiry into the attack has been ordered, officials say.
Shia cleric Allama Mehdi Najfi told Associated Press from his base in Quetta in the south-west: "This attack has spread anger among our people throughout the country, but I appeal to them not to clash with any member of other sects."
About 3,000 Shias protested on the streets of Karachi over the killings.
Ashura marks the death of the Prophet Muhammad's grandson Imam Hussein, an event that led to the split between Shia and Sunni Muslims.