Three Iraqi guardsmen have been beheaded by militants, according to al-Jazeera television.
Wednesday also saw another suspected car bomb in Baghdad
It said it had a video of a militant group calling itself the "Brigades of Iraq's Honorable People" which showed the men being killed.
Three headless bodies were found in the capital Baghdad on Wednesday, Reuters quoted an Iraqi police source saying.
Separately, another group, the Ansar al-Sunna, said it had beheaded a senior Iraqi army officer.
The group posted a video on its website apparently showing the officer being killed.
It said it had abducted Hussein Shunun in Mosul. It accused him of helping US forces in operations there.
The group has claimed responsibility for killing many hostages in the past, including 12 Nepalese earlier this year.
Filipino Tarongoy has been named as one of those kidnapped Monday
The latest violence came as Iraqi police reported a US contractor of Lebanese origin had been seized from his home by gunmen in Baghdad late on Tuesday, police said.
Iraq's interior ministry named the man as Radim Sadeq.
The US embassy has not yet been able to confirm the report.
The abduction is the second this week in the affluent Mansour district. Three foreigners - a Filipino, a Nepali and a US citizen - and three Iraqi guards were kidnapped there on Monday.
In other developments:
The Philippines government confirms that one of its citizens was taken on Monday, naming him as Roberto Tarongoy
- A suspected car bomb explodes near a US convoy on Baghdad's airport road, injuring several Iraqis
Four Jordanian truck drivers are kidnapped near Ramadi west of Baghdad, and two others come under fire
The US military launches two air raids on Falluja, targeting an arms cache and a rebel command post
Gunmen holding hostage Margaret Hassan say in a video on Tuesday they will hand her to militant Abu Musab al-Zarqawi if British troops do not leave Iraq within 48 hours.
Oil industry targets
Earlier on Wednesday, officials said gunmen had shot dead a senior figure in the Iraqi oil ministry on his way to work.
Oil ministry official Hussein Ali al-Fattal died in a hail of bullets as he left his Baghdad home after 0700 local time on Wednesday (0400 GMT).
Iraqi spokesman Assim Jihad told AP news agency that Mr Fattal was a "great loss" to the oil sector.
"He did not care about the threats that many of the ministry officials received," he said. "They are trying to undermine this vital sector in the country."
Meanwhile fires raged near major oil wells near the northern city of Kirkuk after a series of attacks on Tuesday.
The attacks are expected to stop exports for the next 10 days.
Iraq's oil industry has often been targeted by insurgents in recent months.