The move comes as part of an offensive launched on Thursday with an aim to inflict a final defeat on Daesh in a western desert bordering Syria.
Iraqi forces thrust north from the Euphrates Valley into the desert on Saturday, opening up a new front in the drive to flush out fugitive Daesh militants, a commander said.
Daesh has already been driven from all the towns it once held, but Prime Minister Haider al Abadi has said he will not proclaim victory until the group has been cleared from the western desert bordering Syria.
Troops and paramilitaries had advanced into the desert from the east and north on Thursday at the start of an offensive aimed at inflicting a final defeat on the group.
On Saturday, troops and tribal militia pushed north from Al Qaim and Rawa, two Euphrates Valley towns recaptured from Daesh earlier this month, in a pincer movement against retreating Daesh militants, one of the operation's two commanders said.
"It's a matter of linking up with the forces advancing from Nineveh" province in the north, the commander said, asking not to be identified.
"The aim of the operation is to clear the desert right up to the Syrian border and hunt down the terrorists who fled into the desert from the towns that have been liberated."
The Hashed al Shaabi (Popular Mobilisation) paramilitary force, which has played a key role in the offensive, said 100 villages and hamlets had already been cleared of Daesh.
"The battle for the desert is very important because it's from there that Daesh fighters coming from Syria can attack our defence lines," said Hashed number two Abu Mahdi al Mohandis.
In a video posted by the Hashed, Mohandis said the desert was "the last region where Daesh still has a military presence."
He said operations against it were under way over an area of 27,000 square kilometres.
But he warned that their completion would not spell the end of Daesh.
"We must hunt them down in areas that have been liberated and we must arrest them before they slip back into urban areas," said Mohandis, who is widely regarded as the strongman of the Hashed, which is largely composed of Iran-backed Shia militias.
"We must remain in a state of alert," he added. "Security will not be fully assured until we have complete control of the border with Syria."
At the peak of its power in 2014, Daesh ruled some seven million people in a territory as large as Italy, encompassing large parts of Syria and nearly a third of Iraq.
It is now being flushed out of its last desert hideouts in Iraq at the same time as its final pockets of control in Syria face simultaneous operations by Russian-backed government forces and US-backed YPG-led militants.