— Bahrain’s largest opposition movement on Wednesday suspended its participation in talks with the government aimed at ending two and a half years of political turmoil in protest at the arrest of its deputy leader.

Al Wefaq was responding to an announcement by the public prosecutor of the Gulf Arab kingdom that Khalil al-Marzouq would be held for 30 days while being investigated for inciting terrorism in a series of speeches.

In a statement, Al Wefaq, an Islamist group that says it advocates non-violent methods, said it would temporarily boycott a so-called national dialogue aimed at resolving a crisis that began with mass pro-democracy protests in February 2011.

The group would keep its position under constant review “in light of political and human rights developments on the ground.”

The talks began in February but have become bogged down in procedural issues amid an atmosphere of mutual mistrust, with little apparent narrowing of differences on the opposition’s main demand for an elected government.

Persistent unrest since February 2011, when an uprising led by the Shi’ite Muslim majority demanded the Sunni al-Khalifa dynasty give up power, has placed Bahrain on the front line of a struggle for regional influence between Shi’ite Iran and Sunni Saudi Arabia.

Shi’ites have long complained of entrenched discrimination in areas such as employment and public services, despite the denials of the Sunni-led government. The government denies any discrimination.

Al Wefaq demands a constitutional monarchy with a government chosen from within a democratically elected parliament.

The government quelled the 2011 revolt, one of a series of “Arab Spring” upheavals, but protests and clashes have carried on. An international inquiry said in a November 2011 report that 35 people had died during the uprising – mainly protesters – but also included were five security personnel and seven foreigners.

Bahrain’s head of public prosecution, Nayef Yousfi, said police investigations showed Marzouq had spoken at many forums promoting what they described as terrorism, the most recent of which was a speech at Saar district west of the capital Manama on September 6.

At that event, he raised the flag of the opposition group, the February 14 Coalition, said Yousfi. He described the group, a network of activists that uses social media to organize anti-government protests, as a terrorist organization.

Yousfi said Marzouq was interrogated in the presence of his lawyer and subsequently “charged under the Law for Protecting the Community from Terrorist Acts, with inciting and advocating terrorism, and using his leadership position in a legally organized political society to incite crimes.”

The kingdom hosts the U.S. Navy’s Fifth Fleet and is seen in the West as a key regional ally. The government has accused Iran of fomenting unrest in Bahrain, a charge Tehran denies.