Police in Pakistan have released a photo of the man they say bombed a Muslim shrine in Islamabad on Friday.
Islamabad is said to be tense if calm on Saturday
They offered a reward of two million rupees ($34,000; £18,000) for details that could identify the suicide bomber or give information about accomplices.
The Shia community has begun three days of mourning for the victims.
At least 20 people died in the blast at the Bari Imam shrine near the diplomatic quarter in the Pakistan capital, and more than 50 were injured.
Newspapers on Saturday published photographs of the suspect after the blast - with a bloodied unshaven face, thin moustache and curly hair.
"Investigators are trying to identify him. We will soon determine who he is," Information Minister Sheikh Rashid Ahmed told the Associated Press news agency.
Survivors said the bomber joined a congregation of about 1,000 people attending a sermon at the end of a religious festival and then triggered explosive devices strapped to his waist.
The BBC's Zaffar Abbas in Islamabad says that the police investigation into the attack is now in full swing, but has so far yielded few results.
He says the atmosphere across the country is generally calm, with the Shia community left devastated and angry.
That is in contrast to Friday, when hundreds of protesters took to the streets.
Nevertheless, security has been tightened amid fears of renewed tension between the majority Sunni and minority Shia Muslim communities.
The shrine was venerated by both Shias and some in the Sunni community.
President Pervez Musharraf condemned the attack, and appealed for people to unite against "religious terrorism, sectarianism and extremism".
March 2005: 43 Shias killed in a bomb blast in Fatehpur, Baluchistan
Oct 2004: Car bomb in Multan kills 40 Sunnis
Oct 2004: 30 killed in a suicide attack on a Sialkot Shia mosque
May 2004: 20 killed in bombing of Shia mosque in Karachi
May 2004: 15 die in Karachi Shia mosque attack
"Police cannot accomplish the job alone. The government and the law enforcement agencies need full co-operation of the people and it is the duty of everyone to uproot the menace," he said.
UN Secretary General Kofi Annan also condemned the bombing, expressing outrage that civilians have been repeatedly targeted at their places of worship.
US Assistant Secretary of State for South Asia Christina Rocca described the attack as a "tragic event".
Around 60 people wounded in the blast were still in hospital on Saturday and doctors said 15 of them were in critical condition.