Iraq's military said on Friday its forces had advanced on three fronts to begin clearing ISIS militants from the western city of Ramadi, but police and government officials said progress was extremely slow.

The announcement by the joint operations command came as Kurdish forces declared victory over ISIS in the northern town of Sinjar, which could help build momentum in pushing back the hardline Sunni militants elsewhere.

But a suicide bomb attack in Baghdad and a second day of violence between Kurds and Shia Turkmen further north were reminders of the ethnic and sectarian conflicts exacerbated by ISIS's rise.

Iraqi forces appeared better positioned than ever this week to launch an offensive on Ramadi, 100 km (60 km) west of Baghdad, now that months-long efforts to cut off supply lines to the city are having an effect.

The city's fall to ISISin May was the biggest defeat for Iraq's weak central government in nearly a year, dampening its hopes of quickly routing the insurgents from the country's north and west.

Retaking it would provide a major psychological boost to Iraqi security forces after nearly collapsing twice since last year when ISIS seized a third of Iraq, a major OPEC oil producer and U.S ally.

A police officer and a municipal official near Ramadi said federal police had entered a southern district but were moving slowly to avoid explosives they expect ISIS has planted along the roads and in buildings.

An army officer near Ramadi's northern front said troops had started advancing towards the Euphrates along 2 km (1.25 mile) of a main road which would form the final segment of a cordon which security forces have been building for months. He said advances were slowed by roadside bombs.

Separately, a main road linking Baghdad to the northern oil city of Kirkuk was reopened, security sources and local officials said, but violence in and around Tuz Khurmatu which had led militias to block traffic a day earlier continued.

Kurdish and Shia Turkmen fighters in the area have been uncomfortable allies against ISIS since driving the militants out of towns and villages which the Shia-led government in Baghdad claims but the Kurds want as part of their semi-autonomous northern region.

In Baghdad, at least 18 people were killed and 41 wounded when a suicide bomber blew himself up at the funeral of a pro-government Shia fighter.

ISIS said in an online statement it had carried out the attack, though Reuters could not verify the authenticity of the claim.