ABU DHABI — A car bomb targeting Shiite Muslim pilgrims in southern Iraq killed at least 27 people on Thursday, stoking fears of escalating sectarian violence after the authorities threatened to use force against persistent streets protests in the country’s Sunni-majority west.

The explosion in the town of Musayyib, about 60 kilometers from Baghdad, capped a turbulent week dominated until then by demonstrations in the restive Anbar region, home of Sunni militant fighters who once fought U.S. forces and now battle the regime in neighbouring Syria.

With tensions also growing over past weeks between Baghdad and the semi-autonomous Kurdistan region, analysts say Iraq’s fragile post U.S.-occupation political settlement is facing a stern test magnified by the country’s proximity to the deepening conflict in Syria.

“We are at this moment in a kind of tornado,” said Maria Fantappie, an Iraq expert at the International Crisis Group, a non-governmental organization specialising in conflict analysis. “December has shaken completely the political scene – and in a way people did not expect.”

Hours before the Musayyib bomb, Iraq’s government announced the release of 11 female prisoners and pledged to send others to jails in their home provinces, in an apparent response to demands made during a wave of street protests by members of the country’s Sunni minority.

The news came after the Shiite-led government of Nouri al-Maliki, prime minister, had threatened to use force against the demonstrations, which are among the first big street protests seen in Iraq since the early days of the Arab spring almost two years ago.

Ali al-Mousawi, Maliki’s spokesman, said the government’s warning was aimed only at those who might use violence to “exploit the protests to serve their own agenda.” He said the situation in areas such as Anbar was “very sensitive” because there was no control over the movements of weapons or Jihadists across the Syrian border.

“The right to protest is granted in the constitution but the security situation in Iraq is very volatile,” he said. “We are concerned that terror groups like al-Qaeda might use the protests for other purposes.”

Some analysts say a violent struggle between the government and demonstrators could prove a deadly turn of events in a place where Sunni militias fought fiercely against U.S. troops during the 2006-2008 sectarian war.

“It’s a big concern for everybody, not only in Iraq but also in the region,” said Abdulaziz Sager, head of the Gulf Research Centre. “If the demonstrators decide to defend themselves using guns, this could easily lead to a civil war again.”

The demonstrations around Ramadi, the capital of Anbar province and other Sunni areas of Iraq erupted after the arrest last month of bodyguards of Rafia al-Issawi, finance minister, one of the coalition government’s top-ranking Sunni officials. But most analysts say the Sunni dissent has deeper roots in feelings of discrimination since the U.S. invasion of Iraq in 2003 overturned the dictatorship of Saddam Hussein, a Sunni who oppressed both Shiites and Kurds.

Demonstrators near Ramadi this week held banners accusing the government of sectarianism and of holding Sunnis unjustly in its “Persian jails” – a reference to Maliki’s good relations with the Shiite regime in neighbouring Iran, where he used to live in exile. The protesters have also called for a curbing of the de-Baathification law that has purged many Saddam Hussein-era officials from power – a demand the government says will be considered by a parliamentary session on Sunday.

Analysts say Maliki’s administration is for now taking a carrot and stick approach to the protests, confident of its strong control of government security forces but also aware that it is facing challenges to its authority on several fronts.

Moqtada al-Sadr, a cleric and powerful rival Shiite politician, has offered cautious support for the street protests, while the Maliki administration is also at loggerheads with Massoud Barzani, president of Iraqi Kurdistan, in a dispute over oil concession rights that has led both Baghdad and Irbil to mobilise troops at the border of their territories.

— Financial Times

Abeer Allam in Cairo contributed to this story.