An Iraqi refugee living in Jordan casts his ballot Friday at a polling station in a government school in Amman. (Muhammad Hamed/Reuters)

Iraqis living abroad began casting ballots in their homeland's crucial parliamentary elections Friday, a constituency Iraq's Sunni Arab minority hopes will boost its showing.

Thousands stood in lines at polling stations in Syria and Jordan, home to the largest Iraqi expatriate communities. Voting was also being held in more than a dozen other countries around the world, from Australia to the United States.

The United Nations refugee agency estimates that around two million Iraqis are living abroad — the majority of whom fled violence following the 2003 U.S.-led invasion.

A large proportion of those — particularly in Jordan and Syria — are Sunni Arabs who fled the fierce wave of sectarian killings at the height of the Iraq war.

That has made their votes a major focus of attention for Sunni leaders in Iraq, who are hoping a strong turnout among their community will counterbalance a strong vote among the Shia majority for their own religious parties.

Voting abroad will be held for three days, while in Iraq most voters go to the polls on Sunday, choosing a 325-seat legislature. The largest bloc in parliament will try to put together a government to lead Iraq for four key years as U.S. troops withdraw.

In Jordan, a Sunni tribal leader from the western Iraqi province of Anbar, Saad Al-Hardan, warned that after the Americans leave, Iran will try to dominate Iraq — a common fear among Sunnis because of the deep ties between Iraqi Shia parties and Tehran.

"The U.S. occupation will end, but the Iranian one is there to stay. The Iranian influence is significant in parliament and in the government," he said.

The head of the Iraqi election commission in Amman, Nehad Abbas, said turnout out Friday was good, adding that he expects around 180,000 Iraqis in Jordan to cast ballots.

Syria has nearly 800,000 Iraqi refugees, while Jordan's community is estimated as high as 500,000, according to the United Nations High Commissioner for Refugees.

Voting seemed slower in Lebanon, home to a much smaller community of around 50,000 Iraqis.

Early voting marred by suicide blasts

Advance voting started in Iraq on Thursday, and Iraqi election commission member Hamdiya al-Hussaini said that 600,000 people cast their ballots early. Those who took part included security officials, detainees and medical workers and others who might not be able to get to the polls on Sunday.

The early vote was marred by a string of deadly blasts that killed 17 people, highlighting the fragile nature of the country's security gains.

Earlier this week, the UN's representative in Iraq, Ad Melkert, sought to dampen expectations about a large turnout abroad.

He noted that not only do Iraqis have to document their Iraqi nationality but they also have to document the province they come from — a potentially harder task for people who fled their homeland.

Voting is also starting Friday in the United States, Canada, Australia, Austria, Sweden, Germany, Britain, Denmark, Holland, Iran, the United Arab Emirates, Egypt and Turkey.