Iraqi forces recently took control of Iraq's cities as US forces withdrew
Authorities in Iraq's Anbar province have arrested more than 300 suspected insurgents, following a series of recent attacks in the area.
Many of those detained are thought to be former prisoners who had been freed by US forces according to a security pact with the Iraqi government.
Elsewhere in Iraq, five Iranian pilgrims were shot dead near the city of Baquba, police said.
Gunmen opened fire on the pilgrims as they travelled by bus.
Also on Wednesday, the US military said two assailants and one bystander had been killed in Abu Ghraib, west of Baghdad, when a US convoy came under fire.
Deadly attacks increased in Iraq as the US completed its withdrawal from urban areas at the end of June, though the overall level of violence has fallen sharply in recent months.
In Ramadi, the capital of Anbar where Wednesday's arrests were made, three people were killed in a bomb blast outside a restaurant the previous day.
A vehicle ban remains in place in the city.
The pilgrims attacked near Baquba were on their way to Shia holy sites in Iraq and were travelling along a road which links the Iranian border to Baghdad.
A doctor at a nearby hospital told Reuters news agency that survivors had told him how gunmen on motorbikes had stopped the last of three buses before opening fire.
A police official said that security forces escorting the bus had exchanged fire with the gunmen, who fled after the attack.
At least 35 pilgrims were injured in the attack, 65km (40 miles) east of Baquba, in Diyala province.
In April dozens of Iranian pilgrims were killed in a series of blasts in Baghdad and Baquba.
Interior Ministry forces have been protecting pilgrim convoys on the route following those deaths, when as many as 60 Iranian pilgrims died in a suicide bombing at a roadside restaurant.
After Wednesday's attack the wounded were given initial treatment at a local hospital before being sent back to Iran.
Iranian officials condemned the attacks, blaming them on the presence of US forces in Iraq.
Iran's Supreme Leader Ayatollah Ali Khamenei said in a statement on his website that Iraq should "seriously oppose such crimes".
"The growth of the poisonous weeds of terrorism in Iraq will undoubtedly be put on America's criminal record," he added.
Iran blames the US for causing chaos in Iraq, while the US accuses Iran of meddling in the country by supporting Shia militia.