RAMADI, Iraq (Reuters) - Thousands of protesters from Iraq's Sunni Muslim minority kept up a week-old blockade on a key highway on Thursday and readied mass rallies for Friday to demand concessions from Prime Minister Nuri al-Maliki.
Protests flared last week after troops loyal to Maliki, who is from the Shi'ite majority, detained bodyguards of his finance minister, a Sunni. Many Sunnis, whose community dominated Iraq until the fall of Saddam Hussein, accuse Maliki of refusing to share power and of favouring Shi'ite, non-Arab neighbour Iran.
A year after U.S. troops left, sectarian friction, as well as tension over land and oil between Arabs and ethnic Kurds, threaten renewed unrest and are hampering efforts to repair the damage of years of violence and exploit Iraq's energy riches.
"The people want to bring down the regime," chanted some of about 2,000 demonstrators in the Sunni city of Ramadi - an echo of those used abroad during last year's "Arab Spring" and still a rallying cry for mainly Sunni rebels in neighbouring Syria.
Some flew the old Iraqi flag, introduced by Saddam's Baath party and bearing three stars. It was replaced in 2008. Earlier in the week, Syria's rebel flag was also flown at the protests.
The main highway at Ramadi, 100 km (60 miles) west of Baghdad, was barricaded for a fifth day, disrupting transit of government supplies along a key trade route to and from Jordan and Syria. Protesters were, however, letting most trucks, carrying private goods, pass along another road through Ramadi.
There was also a small protest in the northern city of Mosul. Activists, who want changes to laws on terrorism that they say penalise Sunnis, plan bigger rallies on Friday, the traditional day of rest - and protest - in the Muslim world.
"If the government does not deal seriously with the people's demands, we will take our battle to the gates of Baghdad," said Sheikh Ali Hatem Sulaiman, head of the Dulaimi tribe, which dominates Ramadi and the sprawling desert province of Anbar.
Recalling the role the Anbar tribes played in first fighting the U.S. occupation and then allying with U.S. forces and the Baghdad government to contain al Qaeda fighters in the region, the sheikh warned Maliki's administration that Sunnis might resort to violence - though it is unclear how ready they are:
"Just as we fought al-Qaeda and the Americans, we will fight the government inside Baghdad," he said.
Should Friday's protests provide a mass show of force, it may add to concerns that the increasingly sectarian Syrian civil war, where majority Sunnis are battling a ruler backed by Iran, will push Iraq back to the Sunni-Shi'ite slaughter of 2005-07.
Al Qaeda fighters appear to be regrouping in Anbar and to be joining rebel ranks across the border in Syria.
While demands so far focus on the anti-terrorism laws which Sunnis say are being used against them, one lecturer in law at Baghdad University said Sunnis might be emboldened to call for regional autonomy in Anbar and other provinces in the northwest where they are in a majority - a status similar to that of the Kurds, who won Western-backed autonomy from Saddam in 1991.
"I'm seeing greater determination to defy Maliki and if their demands are not met, the call to have their own region will be an inevitable consequence," said Ahmed Younis. "The Kurdish region could become a model for Sunnis in Anbar."
Sunni complaints against Maliki grew louder a week ago when, just hours after Iraqi President Jalal Talabani, a Kurd seen as a steadying influence, was flown abroad for medical care, troops arrested bodyguards for Finance Minister Rafaie al-Esawi.
For many it recalled how Vice President Tareq al-Hashemi, a Sunni, was forced to flee into exile a year ago, just when U.S. troops had withdrawn. Hashemi, sentenced to death in absentia, told al-Hayat newspaper on Thursday that it was "fresh evidence of a plot to exclude Sunni Arabs from the political process".
Maliki has sought to divide his rivals and strengthen alliances in Iraq's complex political landscape before provincial elections next year and a parliamentary vote in 2014.
A face-off between the Iraqi army and Kurdish forces over disputed oilfields in the north has been seen as a possible way of rallying Sunni Arab support behind the prime minister.
Shi'ite rivals to Maliki, notably cleric Moqtada al-Sadr, have also looked to broader alliance, notably by voicing support for the protesters' grievances in Anbar this week.
But anti-Shi'ite rhetoric among them limits the chances for cooperation: "They lost a lot of sympathy by using these sectarian slogans," lawmaker Hakim al-Zamili, a Sadr ally, told Reuters. "I don't expect many Maliki opponents to join them".
An analyst at the Iraq Institute for Strategic Studies also doubted the protests would broaden greatly to threaten Maliki: "We are talking about demands that have a certain geography," said Yahya Qubaisi. "They are not national demands."
(Additional reporting by Raheem Salman and Ahmed Rasheed in Baghdad; Writing by Isabel Coles; Editing by Alastair Macdonald)