The contractors were among more than 1360 Filipinos working at Camp Anaconda in Balad, about 80km north of Baghdad. Another Filipino worker was killed by attackers in Iraq at the end of April.
The Philippines, a staunch ally to Washington, also has about 100 police, soldiers and medical personnel assisting in reconstruction efforts in Iraq.
Two Russians seized in Iraq on Monday are alive and well, but their whereabouts are unknown, their employing company Interenergoservis was quoted by Interfax news agency as saying on Wednesday.
One other Russian engineer was killed when the group came under fire while they were driving home on Monday. Their company has been involved in a power plant project about 30km from Baghdad.
In Baquba, gunmen killed a member of Iraq's US-backed security forces and wounded another in an ambush on Wednesday, witnesses said.
They said assailants opened fire on a car carrying members of Iraq's Civil Defence Corps ICDC in the city 65km northeast of Baghdad, killing one person before fleeing.
The ICDC is a key part of the Iraqi forces which the country's US-led occupiers are trying to establish in the hope they will ease the burden on US troops. Like Iraqi police, they have been the target of frequent attacks by resistance fighters.
The Badr Brigades – the military wing of the Supreme Council for Islamic Revolution in Iraq (SCIRI) staged a demonstration in Basra on Wednesday, celebrating the first anniversary of Muhammad Baqir al-Hakim's return from exile.
Shia challenge al-Sadr
But Aljazeera's correspondent in Basra added the demonstration was also an apparent challenge to Muqtada al-Sadr's al-Mahdi Army. Al-Sadr has been under increasing pressure from Shia groups to calm his rhetoric and use restraint.
The demonstrations took place as a roadside bomb planted between al-Rahma and al-Talimi hospitals rocked Basra and injured an Iraqi.
Zibari says Arab states have yet
to answer call for peacekeepers
Meanwhile, Iraq's foreign minister said on Wednesday Arab states had not yet responded to his request for peacekeeping troops from Arab countries not bordering Iraq.
Foreign Minister Hoshiyar Zibari said he had told Arab foreign ministers at a recent meeting Iraq wanted Arab states to contribute to peacekeeping forces.
"It would be a sign of your solidarity and support," Zibari said he told them.
He told them Arab states' worst fears of civil war and Iraq's fragmentation could fill a security vacuum left by a such a pullout and asked if they would be ready to help.
"But there was no commitment," he added.