At least 40 people were killed in a suicide attack claimed by the radical Sunni Islamic State on a Shiite shrine in northern Iraq, hospital officials said Friday.
Seventy-four were injured in the attack that targeted the shrine of Imam al-Sayed Mohammed bin Ali late Thursday in the town of Balad, around 80 kilometres north of the capital Baghdad.
The attack was carried out by three bombers who posed as members of the pro-government Shiite militia, the Popular Mobilization, and refused to show their ID cards as they entered the shrine, a senior police officer said.
Two attackers detonated their explosive vests at the main gate of the site, the officer added on condition of anonymity.
The third attacker lobbed two hand grenades in the courtyard of the shrine, which was packed with visitors before blowing himself up.
Authorities in the mostly Sunni northern province of Salah al-Din declared a curfew in Balad and two other towns in the province.
In an attempt to defuse sectarian tensions, Governor of Salah al-Din, Ahmed al-Jabouri, called on locals to stand united against the violence.
"Terrorism seeks to sow the seeds of discord and hatred among people of the province," al-Jabouri said in a statement.
Influential Shiite cleric Moqtada al-Sadr, meanwhile, ordered a militia force to go to Balad to protect the shrine and its visitors.
The attack came less than a week after a car bombing, also claimed by Islamic State, killed 292 people in Baghdad's central district of Karada, according to the Health Ministry.
Iraq's top Shiite cleric Ali al-Sistani Friday condemned both attacks.
He accused Islamic State of seeking to foment sectarian strife in the Shiite-majority country and called for "substantial changes" in the top echelons of the security apparatus.
"Being lax with the corrupt and failed [officials] at the expense of blood and lives of civilians has become unbearable," al-Sistani's representative Ali al-Safi said in a sermon at mosque in the holy city of Karbala. "There must be an end to it."
The government was heavily criticized for alleged security inefficiency after Sunday's bombing in Karada - the deadliest such attack in Iraq since the 2003 US-led invasion.
On Friday, al-Abadi sacked chief of the Baghdad Operations Abdul Amir al-Shammari and other security and intelligence officials in the city, state television al-Iraqiya reported.
Since becoming prime minister in September 2014, al-Abadi, a Shiite, has sought to drum up the backing of the country's Sunni minority in the fight to dislodge the Islamic State out of Iraq.
The extremist Sunni Islamic State regards Shiites as heretics.
Late last month, Iraq declared "full liberation" of the western city of Fallujah from Islamic State.
The al-Qaeda splinter group still controls Mosul, Iraq's second largest city.