Dhaka: Veteran Bangladeshi academic-activist Anu Muhammad is no stranger to death threats, beatings, persecution and arrest so when the professor of economics received a chilling text message shortly after midnight, it barely registered.

"Death keeps no calendar, and Ansatullah knows no time!"

But a few hours later, on that same October morning last year, a second SMS pinged - one he could not ignore.

"Say 'yes' to Rampal (a proposed coal-fured power plant) otherwise you will be hacked to death incredibly by us!"

Reporting the threats to police, Muhammad learned that Ansatullah was probably a mistype and referred to Ansharulla or Ansar al Islam, an Islamic extremist group linked to al Quaeda.

The group, implicated in a series of brutal attacks and murders against atheist and gay rights bloggers, had also claimed the murder of a Bangladeshi sociology lecturer in 2014.

Now they seemed to have 60-year-old Muhammad in their sights for his role leading a seven-year campaign against plans to build a $1.5 billion coal-fired power plant in Rampal, southern Bangladesh, on a site teeming with waterways, mud flats and a host of threatened species from crocodiles to pythons.

The protests have turned nasty with at least 20 protesters injured in January and five detained when police launched tear gas and water cannons against anti Rampal protesters.

Activists fear the plant, a joint venture between Indian and Bangladeshi state-run power corporations, will destroy the Sundarbans, one of the world's largest mangrove forests and a UNESCO World Heritage site home to the endangered Royal Bengal tiger and rare Irrawaddy dolphins.

Muhammad - author of more than 30 books - says the mangrove forest is extraordinarily rich in flora and fauna and key to the livelihoods of millions of people.

AIR POLLUTION

"This has also been a huge natural safeguard against frequent cyclone, storm and other natural disasters in the country," he told the Thomson Reuters Foundation.

"The lives and properties of up to four million people who live on it will be threatened if there is no Sundarban."

Scheduled to open in 2021, the plant is expected to burn about five million tonnes of coal each year, pumping out carbon and sulphur dioxide emissions in the process.

Despite local opposition and calls from the United Nations for the plant to be re-located, the government is pushing ahead, saying Bangladesh needs huge amounts of electricity to develop.

Currently, just two percent of power is generated using coal while natural gas reserves are dwindling.

Anwarul Azim, a spokesman for the joint venture company, the Bangladesh-India Friendship Power Company Ltd, told the Thomson Reuters Foundation it was "unlikely to harm theSundarbans" because the plant will be 14 km away from the outer edge of the forest and 69 km from the UNESCO heritage site.

"As a result, the scanty amount of exhaust from the power plant won't be any cause for harm to the Sundarbans," he said.

He said stringent environmental standards had been approved by the Department of Environment and were compatible with World Bank and International Finance Corporation criteria.

Muhammad, however, fears an environmental "disaster".

DANGEROUS LIAISONS

Speaking in his Dhaka home, the economist said he is only too aware of the personal risk he runs in opposing a multi-billion dollar government project, particularly one that is championed by Prime Minister Sheikh Hasina.

"We need to take this risk," Muhammad said. "By destroying a natural huge forest, power and other commercial enterprises reflect a blind development paradigm that puts profit before people and environment."

When committee activists investigated the death threats against him, they told Muhammad the telephone belonged to a member of the Awami Olama League, an Islamist arm of the ruling Awami League. The phone owner denied sending the threats.

Muhammad says he has no intention of giving up.

Over two decades, the professor and his campaign group - the National Committee to Protect Oil, Gas Mineral Resources, Power and Ports - have questioned the role of several multinational resource companies in Bangladesh and their relationships with local partners, government contractors and politicians.

In 2006, they helped scupper a British company's attempt to establish an open coal mine in northwestern Dinajpur district. The company abandoned the project but four lives were lost in the battle to clear farmland.

Muhammad was also integral to a 2007 campaign that quashed multi-billion dollar energy investment plans by the Tata Group.

A year later, when a military-backed caretaker regime was in power in Bangladesh, the professor was threatened with death if he did not stop appearing on television.

In 2009, he was injured when a public rally against an oil exploration project in the Bay of Bengal turned violent.

NETWORK OF ACTIVISM

Erin Kilbride, from the human rights campaign group Front Line Defenders, said governments, companies and armed groups target activists like Muhammad because their deaths not only affect families and friends but disrupt whole activism networks.

"In Bangladesh, for example, following the murders of bloggers and LGBT activists, we documented a sharp decline in advocacy for indigenous peoples, land, and environmental rights as well," she told the Thomson Reuters Foundation.

Muhammad says that deaths in state or police custody are not uncommon in Bangladesh and reflect the breakdown of law and order and legal institutions.

He said the lack of a free media made things even harder with little public awareness about issues like Rampal.

But Muhammad takes heart from the fact that the campaign against the Rampal has linked like-minded activists worldwide, allowing them to share information and support each other.

In January this year, supporters of the Sundarbans joined forces in more than 20 countries, from as far afield as Germany to South Korea, in a Global Day of Protest against the plant.

However the economist says his greatest fear now is the Sundarbans might lose their UNESCO listing, conferred in 1997, with a meeting next month to consider the heritage status.

"If we say yes to the largest, coastal mangrove forest in the world then we must say 'no' to commercial projects harmful for its survival," he said.

"There are many ways to increase the country's GDP but there is no way to reproduce the Sundarbans."