The deployments increased already high tensions in Iraq, adding a long-running Arab-Kurd dispute over territory to a stand-off between Sunni Arab protesters and the country's Shiite-led government that has descended into bloody violence.
Prime Minister Nuri al-Maliki pointed to the civil war in neighbouring Syria as the cause of what he termed renewed sectarian strife in Iraq, while the head of the Sahwa anti-Al-Qaeda militia forces threatened all-out conflict if militants who killed Iraqi soldiers are not handed over.
"After consultations with the governor of Kirkuk, there has been a decision for peshmerga (security) forces to fill the vacuums in general, and especially around the city of Kirkuk," Jabbar Yawar, secretary general of Iraqi Kurdistan region's peshmerga ministry, said in a statement.
Oil-rich Kirkuk province and its eponymous capital are a key part of territory that Kurdistan wants to incorporate over strong objections from the federal government in Baghdad, a dispute diplomats and officials say is a major threat to long-term stability.
Yawar said the peshmerga deployments were aimed at combating militants and protecting civilians, but Iraqi army officers ascribed other motives to the moves.
"They want to reach (Kirkuk's) oil wells and fields," Staff General Ali Ghaidan Majeed, the commander of Iraqi ground forces, told AFP.
He said the deployments were a "dangerous development" and violated an agreement that peshmerga forces and Iraqi soldiers would man joint checkpoints.
Another high-ranking Iraqi officer told AFP that "after the latest movements of the peshmerga forces, the army is on alert."
"The army sees the move of the peshmerga as a (political) manoeuvre and not to fill any vacuum."
The deployments came amid a wave violence that began on Tuesday when security forces moved against Sunni anti-government protesters near the northern Sunni Arab town of Hawijah, sparking clashes that killed 53 people.
Subsequent unrest, much of it apparently linked to the Hawijah clashes, killed dozens more and brought the death toll to more than 215 on Saturday.
The violence is the deadliest so far linked to demonstrations that broke out in Sunni areas of Shiite-majority Iraq more than four months ago.
The Sunni protesters have called for Maliki's resignation and railed against authorities for allegedly targeting their community, including what they say are wrongful detentions and accusations of involvement in terrorism.
Maliki said on Saturday that sectarian strife "came back to Iraq, because it began in another place in this region," in an apparent reference to Syria.
The civil war in neighbouring Syria pitting mainly Sunni Muslim rebels against the regime of President Bashar al-Assad, a member of the Alawite offshoot of Shiite Islam, has killed more than 70,000 people.
Sunni-Shiite sectarian violence in Iraq, which peaked in 2006 and 2006, killed tens of thousands.
"Sectarianism is evil, and the wind of sectarianism does not need a licence to cross from a country to another, because if it begins in a place, it will move to another place," Maliki said.
He also called in a statement for anti-government protesters to "expel the criminals who targeted Iraqi army and police forces," after five soldiers were killed near a protest site.
And Iraqiya state television quoted Sahwa chief Sheikh Wissam al-Hardan as saying that if those who have killed soldiers are not handed over, "the Sahwa will take the requested procedures and do what it did in 2006."
Sahwa militiamen fought pitched battles against Sunni militants from 2006, helping to turn the tide of the Iraq war.
Clashes between gunmen and Iraqi forces left five soldiers dead and one soldier and a gunman wounded on Saturday near the site of a long-running anti-government protest near Ramadi, west of Baghdad, while a sniper killed a policeman in the city, sources said.
The killings came after a Sunni cleric, Sheikh Hamed al-Kubaisi, called in a sermon at the protest site on Friday for the creation of an army to defend Sunnis.
Gunmen also shot dead two football players in Fallujah west of the capital, police and a doctor said, and an AFP journalist there said armed men were patrolling the city in cars.
And five Sahwa militiamen were killed when gunmen attacked a checkpoint south of Tikrit, police and a doctor said.