Iraq's Christians, markedly fewer in number following attacks on their minority community, are increasingly fearful in the face of a rise in sectarian tensions after the withdrawal of US troops.

Estimated to number more than one million before the US-led invasion of 2003, living primarily in Baghdad, the main northern city of Mosul, and the disputed oil hub of Kirkuk, some two-thirds of the population are estimated to have fled since, with more continuing to leave the violence-wracked country.

Their plight was highlighted by an October 31, 2010, assault on a Baghdad church by Al-Qaeda that left 44 worshippers, two priests and seven security force members dead. According to some accounts, the attack only accelerated the exodus.

"We have concerns about the US withdrawal, despite the security forces saying it will be safe," said Louis Sako, Chaldean archbishop of Kirkuk and Sulaimaniyah, the latter of which lies in the autonomous Kurdish region.

"There has been a failure to ensure the safety of Christians -- the security forces are not sufficiently prepared to ensure the protection of Christians. Even though we have repeatedly asked to raise the level of security, the results are not encouraging."

US troops completed their withdrawal on Sunday, leaving security in the hands of an Iraqi force more than 900,000-strong.

Officials insist it is able to maintain internal security, although they openly acknowledge it still lacks the means to defend Iraq's borders, airspace and territorial waters.

That claim was dealt a blow on Thursday when more than a dozen bombings in Baghdad killed 60 people, with violence elsewhere in the country claiming another seven lives.

The attacks only served to raise sectarian tensions amid a worsening political dispute that has seen Iraq's Shiite Prime Minister seek to sack his Sunni Arab deputy, and authorities issue an arrest warrant for the Sunni vice president on charges he ran a death squad, accusations he denies.

"I am only staying in Kirkuk temporarily -- I am waiting to leave at any second," said Salvan Youhanna Matti, a 59-year-old retiree whose three sons have left Iraq for Belgium, Sweden and Lebanon respectively.

"Christians who are leaving Baghdad for Kirkuk or Kurdistan consider those places just temporary stops before they leave for good. The future is unknown, and sectarian and religious conflict hurts our confidence in the situation, especially after the US departure."

Despite assurances of security from local leaders, and proclamations from top officials that protecting Iraq's Christians is a priority, violence targeting the minority still occurs.

Although the October 2010 attack was the deadliest against the country's Christian population since 2003, targeted assassinations and kidnappings still occur, albeit less frequently.

"While Iraqis from all ethnic communities and religious denominations suffered from violence in the years that followed the US-led occupation, smaller minority communities, especially non-Muslims, have been particularly vulnerable," Human Rights Watch (HRW) noted in a February 2011 report.

It noted that "the government... has not taken sufficient measures to bolster security in areas where minorities are particularly vulnerable to attacks."

According to Sako, 57 churches and houses of worship in Iraq have been attacked since the invasion, with more than 900 Christians killed and more than 6,000 wounded.

While those figures pale in comparison to the nationwide violence -- British NGO Iraq Body Count says more than 100,000 civilians have been killed in all -- HRW noted that because minority communities in Iraq lack "militias and tribal structures to defend themselves, a disproportionate number have fled."

One Christian leader in Baghdad said that, along with tensions in Iraq, the minority group was also watching developments elsewhere in the Middle East with unease.

"The coming years will be very difficult for Christian groups in the Middle East and the Arab world, there will be challenges for how to secure them, and protect their rights, privacy of religion and traditions," said Saad Serup Hanna of Baghdad's Mar Yusuf Church.

"I don't know how mature the political leaders and politicians of the Arab Spring are to understand this challenge," he added, referring to fears among Christians that a rise to power of Islamists in countries with deposed dictators such as Egypt and Libya could imperil minority communities.

Voicing concerns about tensions between the region's Sunni and Shiite communities -- Shiite-majority Iraq is home to a Sunni minority that dominated Saddam Hussein's regime -- in the wake of the Arab Spring, Hanna noted: "The situation is moving towards a conflict between the two blocs of Islam.

"Christians are caught in between."