A US citizen, a Nepali and four Iraqis have been kidnapped at gunpoint from their office in Baghdad, the country's interior ministry says.
"They stormed the villa with automatic rifles and rocket-propelled grenades," a police source told Reuters news agency. "They had no chance."
Earlier on Monday, gunmen assassinated the deputy governor of Baghdad, Hatem Kamil Abdul Fatah, in a drive-by shooting in the south of the city.
The attack came as efforts began to register voters for January's polls.
The six men were seized from the offices of the Saudi Arabian Trading and Contracting Company in the Mansour district of Baghdad after a brief shoot-out.
The kidnappers struck at 1735 (1435 GMT) as many Iraqis were ending the Ramadan dawn-to-dusk fast. Three guards were inside eating at the time.
The only guard who remained at his post outside the building killed one of the attackers, but was immediately gunned down himself, according to the company's lawyer.
The three other guards were among those taken hostage.
In other developments:
- US forces pound suspected insurgent positions in Falluja as they prepare for what is expected to be an imminent assault on the city
- Heavy clashes continue in Ramadi between US troops and insurgents, claiming at least six lives according to hospital officials
- Iraq's President Ghazi Yawer says he completely disagrees with the US plans for an offensive in the rebel stronghold of Falluja.
- American troops continue their build-up in Iraq, with the arrival of new forces taking the total US military presence to about 142,000 soldiers
Dozens of foreigners have been seized in Iraq in recent months.
Margaret Hassan, a charity worker for Care International, was taken hostage on 19 October while on her way to work in Baghdad.
She was last seen on a video broadcast on al-Jazeera TV on 27 October.
Baghdad's deputy governor was attacked in his car
A Briton, Kenneth Bigley, and his US colleagues Eugene Armstrong and Jack Hensley were all taken hostage from their house in September, in the same Mansour district where the latest hostages were taken.
All three men were killed.
On Sunday Japan confirmed that a headless body found in Iraq was that of 24-year-old hostage Shosei Koda.
Baghdad's deputy governor was killed on Monday when his car was rammed by attackers as it went past a mosque, the BBC's Alastair Leithead reports.
Gunmen opened fire, wounding two of Mr Fatah's bodyguards, in the attack in the southern Dora district of Baghdad.
An Iraqi militant group, the Army of Ansar al-Sunna, has claimed responsibility for the killing.
Meanwhile a six-week period began during which Iraqis wanting to vote or run for election have to register in 550 centres across the country.
Our correspondent says the centres have been set up in places where Iraqis receive food rations in the hope that people will not feel threatened, and to reduce the risk of targeted attacks.
But militant groups have made threats against those working on the elections, he adds.
The security threat has led to increased troop levels in perceived danger spots.