Members of Tunisia's main ruling Islamist party called for a rally in the capital on Saturday, a day after police clashed with protesters at the funeral of murdered opposition figure Chokri Belaid.
The shooting of the leftist leader and outspoken critic of the Islamist-led government by a lone gunman on Wednesday plunged Tunisia into new post-revolt turmoil as political tensions and division within the Ennahda party itself intensified.
Armoured vehicles and troops were deployed on Saturday along Habib Bourguiba Avenue, the epicentre of the 2011 revolution that toppled autocratic president Zine El Abidine Ben Ali and unleashed a wave of Arab world uprisings.
The Ennahda demonstration was to take place on the landmark boulevard at 1300 GMT, the party said in a statement.
The protest would "defend the legitimacy of the national constituent assembly," in which the Ennahda-dominated coalition holds a majority, and would "fight against (the political) violence" it said the opposition is using.
The opposition has accused Ennahda of assassinating Belaid, after months of simmering tensions between liberals and Islamists over the future direction of the once proudly secular Muslim nation.
Ennahda has flatly denied involvement in the killing, which has laid bare divisions within the ruling party and inflamed anti-Islamist sentiment.
On Friday night, protesters torched Ennahda's headquarters in Sidi Bouzid, the birthplace of the uprising just over two years ago, as well as the office of an Islamist NGO in Souk Jedid, 17 kilometres (11 miles) away.
They also set fire to three administrative buildings in the volatile region, witnesses told AFP.
Islamist Prime Minister Hamadi Jebali's attempts to form a new government of technocrats have been rejected by his own parliamentary bloc, stoking uncertainty as political infighting delays a deal on a new constitution.
Jebali first announced the proposal on Wednesday amid public outrage at Belaid's murder, and insisted late on Friday that he was committed to the planned reshuffle.
"I stick by my decision to form a government of technocrats and I would not need the support of the constituent assembly," he was quoted as saying by the TAP news agency.
Sahbi Atig, Ennahda's leader in the national assembly, criticised Jebali for not consulting his own party, while another top Ennahda official, Abdelhamid Jelassi, insisted on the need to maintain the legitimate coalition government.
Fugitive Salafist leader Abu Iyadh, who heads the radical Islamist group Ansar al-Sharia and is accused of organising a deadly attack on the US embassy last year, warned Ennahda that compromising with secular parties was "political suicide."
The Tunisian League for Defence of Human Rights said threats and intimidation were continuing under the Ennahda-led government, and called for politicians to be protected.
Tens of thousands of protesters took to the streets on Friday for Belaid's funeral, and clashes with police who fired tear gas led to 132 arrests, the interior ministry said.
Belaid, 48, who was shot dead as he left home for work on Wednesday, had repeatedly spoken out against the ruling Islamists.
As Friday's procession began its three-and-a-half kilometre (two-mile) journey to the cemetery, Belaid's widow Besma held up two fingers in a victory sign as a chant of "The people want a new revolution" rang out.
"We lost a great hero," Beji Caid Essebsi, a former premier and now a centre-right opposition leader, told AFP.
As a general strike called by the powerful 500,000-strong General Union of Tunisian Workers (UGTT) took hold, troops were deployed in Zarzis in the south and Sidi Bouzid.
The strike was believed to be the biggest since January 14, 2011 -- the day Ben Ali fled to Saudi Arabia, where he remains in exile.