DHAKA (Reuters) - One night in February, Rajib Haider was set upon near his Dhaka home by five knife-wielding youths. His face was so lacerated that a relative who found the body wasn't sure it was him until he called Haider's cellphone and heard it ring inside a pocket.
Haider was a blogger, one of hundreds in Bangladesh demanding the death penalty for Islamist leaders accused of wartime atrocities, whose grisly murder swelled the crowds at student-led rallies many hailed as a "Bangladesh Spring".
But now, a radical pro-Islam movement has emerged to counter the students it sneers at as "atheist bloggers".
Known as Hefajat-e-Islam, it has given the government until May 5 to introduce a new blasphemy law, reinstate pledges to Allah in the constitution, ban women from mixing freely with men and make Islamic education mandatory - an agenda critics say would amount to the 'Talibanisation' of Bangladesh.
The clash of ideologies could plunge Bangladesh into a cycle of violence as the two main political parties, locked in decades of mutual distrust, exploit the tension between secularists and Islamists ahead of elections that are due by next January.
"This is a confrontation between secular and conservative orthodox interpretations of religion," said Muhammad Zamir, a former career diplomat and now a newspaper columnist.
Blaming the opposition Bangladesh Nationalist Party (BNP) for encouraging Hefajat to square off against the students, he said "they now realise they have opened Pandora's box".
Already dozens of people have been killed in clashes this year, mostly between Islamist party activists and security forces, and a series of general strikes called by opposition parties is starting to bite into the Muslim-majority country's fragile economy.
What is now Bangladesh became part of Pakistan at the end of British colonial rule of India in 1947. The country, then known as East Pakistan, won independence with India's help in December 1971 following a nine-month war against the rest of Pakistan.
The trigger for this year's spasm of unrest came in February when a tribunal set up by the government to investigate abuses during the war sentenced a leader of the Jamaat-e-Islami party to life in prison, sparing him execution.
Jamaat, an Islamist ally of the BNP that opposed independence from Pakistan, denies accusations that some of its leaders committed murder, rape and torture during the conflict.
Wrangling over a war that ended 42 years ago might puzzle outsiders, but it underlines the unresolved rift within this South Asian country of 160 million between secular nationalism and a belief that Islam is the defining core of the state.
The tribunal's decision not to sentence Abdul Quader Mollah to death sparked public outrage that was fuelled by secular activists who used blogs and social media websites to call for mass protests.
Tens of thousands poured into the Shahbag area of central Dhaka, staging rallies and vigils. The rise of their movement was soon referred to as a "Tahrir Square" moment, after the scene of protests in Cairo that led to the overthrow of Egyptian strongman Hosni Mubarak in 2011.
Imran H. Sarker, who gave up his full-time job as a physician to lead the movement, says that some 60,000 Internet activists have now united under the "Shahbag" banner against war crimes and Islamic fundamentalism.
His group now also wants the government to ban Jamaat, whose student wing ordered the slaying of blogger Haider, according to the confessions of five students who say they carried it out.
"They don't even love this country," Sarker, a softly spoken 29-year-old, told Reuters at a medical university in Dhaka, railing against the Islamist party. "When we play cricket against Pakistan ... they take along a Pakistani flag."
He denied charges that "Shahbag" enjoys backing from Prime Minister Sheikh Hasina's party, the centre-left Awami League, which critics say is exploiting the war tribunal to win votes.
However, his movement's decision to target Jamaat convinced many that Sarker is a pawn of the government. It shifted the narrative of the public quarrelling from war crimes to religion, and it spurred a backlash from Islamist forces.
Blood-letting erupted across the country at the end of February when the war crimes tribunal condemned a top leader of the Jamaat party to hang.
The army was deployed after furious Jamaat activists attacked police with crude bombs, swords and sticks, burnt down houses of Awami League leaders and Hindus, and raided Hindu temples. At least 30 people were killed on the day of the ruling alone, and the toll ratcheted up over the next few days.
The emergence of Hefajat-e-Islam since then was the Islamist answer to "Shahbag", whose momentum appears to have fizzled out. Over 100,000 people massed in central Dhaka on April 6 to rally behind the new movement, whose name means 'protector of Islam'.
Among the speakers at that rally was Habibur Rahman, head of a madrasa - or religious school - who told local media after a trip to Afghanistan in 1998 that he had met former al Qaeda leader Osama bin Laden and praised "the total victory of Taliban and establishment of an Islamic state in Afghanistan".
One of Hefajat-e-Islam's leaders is Mufti Fayez Ullah, who spoke to Reuters from a mosque that is set among the narrow bustling streets of old Dhaka and hums with the sound of boys reciting from the Koran, Islam's holy book.
"We have been termed as Taliban, but this is absolutely false, baseless and nothing but propaganda against us," he said. "But the Shahbag people are against Islam. They humiliate men with beards and caps. It cannot be tolerated."
He said Hefajat-e-Islam's supporters would bring Dhaka to a standstill on May 5 if the government did not meet a list of 13 demands, which include the call for a new law against blasphemy.
Several more verdicts are likely to be handed down by the war crimes tribunal in coming months, keeping alive tensions that analysts say the government and its arch-foes - the BNP and Jamaat - will try to use to their advantage as elections loom.
For now, the bloggers vs. Islam feud has diverted attention from a stand-off between Prime Minister Hasina and BNP leader Begum Khaleda Zia over whether to install a caretaker authority to ensure a free and fair election.
Both heirs to political dynasties, Hasina and Khaleda have rotated as prime minister since 1991 amid unending enmity.
Diplomats in Dhaka say the interim administration row will come to a head around September.
If that impasse is not broken, the BNP may boycott the poll, unleashing fresh unrest - or there could be a repeat of 2007, when the army stepped in and installed a provisional government to crack down on political thuggery and violence.
Additional reporting by Ruma Paul and Serajul Quadir; Editing by Nick Macfie