Iraqi Prime Minister Nouri al-Maliki personally ordered the arrest of a presidential guard said to have shot dead an Iraqi journalist after a quarrel.
Mohammed Bedaiwi, a university professor and Baghdad bureau chief of Radio Free Iraq, shot in the head on Saturday following an argument with an officer who works for President Jalal Talabani.
The incident took place at a checkpoint near the presidential compound, in the Jadriya area of the Iraqi capital Baghdad, while Bedaiwi was on his way to work.
The Associated Press news agency, citing police and state television, reported that Iraqi security forces went to the compound after the shooting to arrest the officer, who has not been named.
Talabani's office issued a statement expressing sorrow for Bedaiwi's death. "This act runs against all the values of the Presidential Brigade...We stress that the perpetrator will stand trial and receive his fair punishment," it said.
State television showed Maliki arriving at the crime scene, where he said: "All the people behind this should stand trial. Blood for blood and this is a violation of the law."
Iraq is one of the deadliest places in the world for journalists, according to the Committee to Protect Journalists.
Bombings in Tikrit
Earlier on Saturday a double bombing rocked an Iraqi city north of Baghdad, leaving at least seven people dead.
The attack occurred after a roadside bomb exploded in a commercial street in the northern city of Tikrit. Minutes later, a car bomb struck policemen who had arrived to inspect the first blast.
The officials said five policemen and two civilians were killed and 18 people were wounded. A medical official confirmed the casualty figures.
Saturday's blasts followed a day of attacks that killed and injured scores of people across the country.
The deadliest incident on Friday occurred in the village of Injanah, 55km north of Baquba, when an explosive-laden tanker was driven into the federal police headquarters, killing at least 15 people.
Violence has spiked in Iraq since last April, in a surge unseen since 2008, with the relentless bloodshed presenting the government with a serious challenge.