Talking to Aljazeera, Iraqi National Security Adviser Muwaffaq al-Rubayai on Monday said all evidence pointed to Abu Musab al-Zarqawi and his group.
"Through our investigations, we have gained solid facts proving that al-Zarqawi's group has carried out this horrible act against the Iraqi people," he said. "We have no doubt it was al-Zarqawi's group," he added.
"The Iraqi interim government denounces this act and these terrorist explosions against civilians in Baghdad and Mosul and against Christian and Muslim citizens," al-Rubayai said.
"A cowardly group is behind these actions, aiming to break up the Iraqi national unity and to drive a wedge between Muslims and Christians just as it used to do between the Sunni and Shia," he added.
Government blames al-Zarqawi
group for the blasts
"We think those who carry out such acts are not only enemies of God and their country, but also enemies of the Iraqi people," al-Rubayai said.
"The Iraqi government reassures all sections of the Iraqi people that it will track the criminals wherever they are," he said. "We promise our people they will be judged," he added.
In Baghdad, the patriarch of the Chaldean church in Iraq urged Muslims and Christians to stand shoulder to shoulder on Monday, after orchestrated bombings against churches killed more than a dozen people and wounded 50.
"Christians and Muslims must stand together for the good of Iraq because we are one family," Emmanuel Delly said.
He said he would address the same appeal in a letter to the caretaker Iraqi government.
"Christians and Muslims must stand together for the good of Iraq because we are one family"
patriarch, Chaldean church, Iraq
Delly forgave the perpetrators of the attacks, for which no group has yet claimed responsibility. "The Lord pardons them and illuminates their spirit for the good of the Christians and Muslims in Iraq," he said.
In Najaf, Iraq's revered Shia Muslim spiritual leader on Monday condemned the bomb attacks against churches and called for national unity to quash the violence.
"In the criminal campaign targeting Iraq's unity, stability and independence, a number of churches were targeted in Baghdad and Mosul that resulted in scores of innocent casualties," said a statement from the office of Ayat Allah Ali al-Sistani.
"We denounce and condemn those terrible crimes... We should all be working together as a government and a people in order to put an end to the attacks against Iraqis," it said.
"We stress the need to respect the rights of Christians in Iraq and those of other religious faiths and their right to live in their home, Iraq, peacefully," it added.