IN MUVATTUPUZHA, INDIA Wearing jeans and leaving her auburn hair uncovered never created problems for Rayana Khasi, a 22-year-old Muslim engineering student in the coastal state of Kerala.

But then came the threats. About two months ago, members of the Popular Front of India, a fast-growing Muslim political and social organization in Kerala, allegedly started sending text messages to her saying, "You're committing blasphemy."

They admonished her publicly in her home town of Kasaragod, confronted her family and pelted her car with stones, she said.

"Many women here are now listening to them and covering. But this is India, not Afghanistan," said Khasi, who has moved to a different city and changed her cellphone number several times as Indian authorities investigate her charges.

For centuries, Kerala has been known as "God's country," and generations of Muslims, Christians and Jews were warmly welcomed by Hindus here. One of India's most religiously diverse states, Kerala has rarely experienced the religious violence that has flared in other parts of the country.

But the Popular Front's rise here is stirring concern as a growing number of its young members embrace a radical brand of Islam. Authorities say they fear that the group has become an example of how extremism can creep into a society, even one in which the vast majority of Muslims are not conservative.

Intelligence authorities say the government is investigating threats against women such as Khasi and other attacks, including a case in which Popular Front members are accused of severing the right hand of a Christian professor for what they felt was a slight against Islam. More than 25 men have been arrested in the case, and trials are set to begin soon.

The Popular Front, which has denied involvement in any attacks, says it sets out to defend minority groups and lower castes. But officials say they are troubled by the group's connection to the Students Islamic Movement of India (SIMI), which was banned in 2001 for supporting terrorism and accused of involvement in the 2003 train bombings in Mumbai that killed 10 people. Many Popular Front members were once part of SIMI.

The government has struggled with how to respond to the Popular Front because it often voices ideas through protests, a right "available in a democratic society and provided for by the Indian constitution," said Hormis Tharakan, former chief of India's intelligence agency, the Research and Analysis Wing. "But it's the propensity toward violence that is most worrying."

The group's emotional messages that mention the Palestinians and such common Muslim grievances as the wars in Iraq and Afghanistan resonate among Kerala's highly educated population, which tends to be more aware of global issues. And nearly every household has at least one male working in Persian Gulf countries, a migration that began during the oil boom of the 1980s.

"Once there, some Keralites undergo a spiritual reawakening in countries that espouse a far stricter version of Islam," said M.G.S. Narayanna, former chief of the Indian Council of Historical Research, who is based in Kerala. "They are told that Indian Islam is not pure and they should learn Arabic, study the Koran in Arabic. That is how it starts. Then they start learning about what they are told is hatred and injustice against Muslims around the world."

T.J. Joseph, the professor whose right hand was cut off in July, was allegedly attacked by a mob of Popular Front recruits.

He said they accused him of mocking the prophet Muhammad in an exam paper in which he called a delusional man who talked to God "Mohammed."

"I never thought this violence could happen in Kerala," said Joseph, sitting in his living room and struggling to write with his stiff, swollen hand, which was reattached after two 16-hour surgeries. He was also stabbed in a leg during the attack and now uses a wheelchair.

Joseph said he had not intended to insult the prophet.

Since the attack, three police officers guard the house 24 hours a day. They sleep on cots on the veranda.

Many of those accused in the attack live nearby, including the Popular Front's youth education counselor, Anas, who goes by one name.

Anas, 30, who denies any link to the attack, made headlines when he won a local political seat in October while he was still in jail. He is out on bail.

"No one should support violence. But the professor used bad words against Islam, and young people can't always suppress their feelings," Anas said. Like many young men in Kerala, he worked in Qatar for several years.

The Popular Front's national executive, P. Koya, said the suspects in the attack "were rogue elements."

"Even if some of our activists were involved, it had nothing to do with our policies," Koya, a founding member of SIMI, said in an interview at the party's office in the city of Kozhikode.

Dressed casually and surfing the Internet as he spoke, Koya said the Popular Front is combating a sharp rise in attacks against Muslims by Hindu extremist groups, or "saffron brigades." He pointed to recent cases in which Hindu extremists are being investigated for alleged acts of terrorism, including a series of bomb blasts in 2006 in the state of Maharashtra. At least 37 people were killed, mostly Muslim pilgrims.

"We are defending ourselves against Hindu terrorists and all acts against Islam," he said.

Nearby, several members agreed, saying that chopping off the professor's hand served as a lesson for others.

After Joseph was attacked, police raided the Popular Front's offices and found literature and videos about Taliban-style executions and the severing of limbs as punishment for crimes, investigators said.

"They are trying to radicalize the Muslim community, but many Muslims have a good life here and their problems are not the same as those in Gaza or Afghanistan," said P. Vijayan, the Kerala police commissioner.

N.P. Ashley, an English professor who is Muslim and an expert on Islam in Kerala, said that "the problem is the majority of Indian Muslims are completely against extremism, but they are also completely faceless and need dynamic leaders."

Vijayan, the police commissioner, said he hopes to help build that leadership through the Student Police Cadet Project, a program he has launched in 130 schools across the state. He also reaches out to private Muslim schools in the area.

On a recent day, students in the program marched proudly in the sun, wearing fresh police uniforms. The Muslim students said they felt empowered when they helped fellow Muslim Indians, many of whom are afraid of the police.

"I want Muslim youth to feel a part of India," said Mohammed Ahmed, a 16-year-old Muslim student. "We need to help fight terrorism."