* Two weeks of protests close major highway to Jordan, Syria
* Syrian crisis fueling worries over Iraq's sectarian mix
* Power-sharing government deadlocked since U.S. troops left (Updates with parliamentary motion, more details)
By Patrick Markey and Raheem Salman
BAGHDAD, Jan 9 (Reuters) - Opponents of Iraqi Prime Minister Nuri al-Maliki on Wednesday demanded he appear before parliament for questioning in a second attempt to force a vote of no confidence, as the Shi'ite leader faced Sunni Muslim protests.
Thousands of demonstrators have taken to the streets in Sunni strongholds across Iraq for more than two weeks, increasing fears that turmoil in neighbouring Syria may help tip Iraq back into the broad sectarian violence it suffered a few years ago.
Maliki's rivals among Sunni, Shi'ite and Kurdish blocs remain sharply divided, and failed last year to win required approval from the president or support in the 325-member Council of Representatives for a vote of no confidence.
But popular unrest and parliamentary pressure may combine to become a major test for Maliki, a Shi'ite nationalist whom many Sunni leaders accuse of marginalising their sect and amassing too much power a year after the last U.S. troops left.
Lawmakers collected more than the 25 signatures required to call Maliki to appear in parliament to be questioned on alleged violations of the constitution and of a power-sharing agreement.
"The first step is questioning him and we presented a request today," said Sunni-backed Iraqiya party lawmaker Jaber al-Jaberi. "The next stage will be a vote of no confidence if we can get enough votes."
A spokesman for Maliki did not immediately return calls seeking comment on the motion.
Iraqi troops earlier on Wednesday shut the key Traibil border post with Jordan in the Sunni heartland province of Anbar, where protests erupted in late December after authorities arrested the bodyguards of a Sunni finance minister.
Several thousand demonstrators are camped out on the highway near the Sunni stronghold of Ramadi, about 100 km (60 miles) west of Baghdad, before the point at which it splits into a road leading to Syria and another to Jordan.
"Our work has halted completely," Colonel Mahmoud Mohammed Ali, deputy chief of border police at the crossing, told Reuters by telephone. "There are no trucks, no passenger cars, and officials at the gate are not working."
Protests broke out in December after Finance Minister Rafaie al-Esawi's bodyguards and staff were detained on terrorism charges. Sunni leaders saw the arrests as part of a sustained crackdown on their sect by Iraq's Shi'ite leadership.
Sectarian tensions remain raw in Iraq, which endured years of Sunni-Shi'ite bloodshed after the U.S.-led invasion that toppled former strongman Saddam Hussein in 2003.
Many Sunnis say they feel sidelined since elections in a post-Saddam Iraq empowered majority Shi'ites, while Shi'ite leaders point to the presence of Sunnis in important posts like speaker of parliament as evidence that power-sharing is genuine.
CRISIS AFTER CRISIS
Violence has eased, but the government, made up of Shi'ite, Sunni and ethnic Kurdish blocs, has been deadlocked over how to share power since American troops left in December 2011.
Complicating the attempts to ease Sunni protests, the Arab-led central government in Baghdad is also caught in a standoff over oil with autonomous Kurdistan in the north, where ethnic Kurds run their own regional government.
The arrest of Esawi's men came a day after President Jalal Talabani, a veteran Kurdish statesman who has long mediated among parties, went abroad for medical treatment after a stroke.
Maliki, who spent years in exile fighting Saddam and after 2003 helped purge members of the former Sunni ruler's outlawed Baathist party, has made small concessions to the Sunni protesters, but these have failed to end the unrest.
"It is in the interest of the government for people go out and demonstrate to express their rights," he said on Wednesday. "But some want confrontation between police and demonstrators to say there is no liberty or democracy."
Sunni leaders and tribal sheikhs' demands range from Maliki's removal to release of detainees and the suspension of an anti-terrorism law that Sunnis believe has been abused by authorities to target their sect unfairly.
Local Anbar officials accused the central government of trying to choke the local economy by closing the Jordan crossing, in an attempt to put pressure on protesters.
Jordan is the country's fourth-largest trading partner, with Iraq importing around $850 million in goods from its neighbour last year, according to a local business council.
"This targets Anbar's population," said Sadoon al-Shaalan, deputy chief of Anbar provincial council.
"This step will impact the economy of the province in general. It targets the livelihood of the people."
A year ago, another crisis erupted after authorities sought the arrest of Sunni Vice-President Tareq al-Hashemi, accused by officials of running death squads. He fled the country and was later sentenced to death in absentia. (Additional reporting by Aseel Kami; Editing by Andrew Roche)