A previously unknown Islamic militant group claimed Thursday to have used explosive-laden bicycles to plant bombs that tore through this historic Indian city, warning in an e-mail of more attacks on popular tourists sites.

The e-mail, a copy of which was obtained by The Associated Press, came with a document that demands India stop working with the United States and Britain or "face more attacks at other important tourist places."

Authorities said they were investigating the videos and the document to determine if they were indeed sent by those behind Tuesday's attack, which killed 61 people.

"Some of the footage may have been meant to mislead," said Vasundhara Raje, the chief minister of Rajasthan state, where Jaipur is located. "Intelligence officials are looking" at the videos and the e-mail, which were originally sent to Indian television channels.

The e-mailed videos show a bicycle with an alleged bomb strapped to it parked in a crowded market. Investigators believe most of the bombs were placed in bags left on bicycles, which police have traced to two shops in Jaipur's old city, said Pankaj Singh, the city's inspector-general of police.

Police have also released a sketch of a man in his early 20s who is suspected of buying the bicycles, and have questioned nearly a dozen people. But no arrests have been made, Singh said.

The e-mail also came with an attached Microsoft Word document that is purportedly written by a Guru al-Hindi, who claims to be from a previously unknown group calling itself the Indian Mujahedeen.

"This letter is an open warning to India (to) stop supporting (the) U.S. in the international arena, and if you do continue then get ready to face more attacks at other important tourist places," wrote Guru-Al-Hindi, which is a blend of Hindi and Arabic that means teacher of Indians.

The attack came at the height of the Indian summer when temperatures in Jaipur regularly top 100 degrees and there are few tourists in town. No foreigners were reported killed or wounded in the bombings, which killed Hindus and Muslims alike.

Oddly, the message also included the password for the French Yahoo account used to send the e-mail.

The oldest e-mail currently in the account's inbox was received about two hours after the first of nine bombs went off. Other more recent messages include queries from Indian journalists and a number of scam e-mails requesting help moving large sums of money from fictitious African banks.

Still, authorities said they were taking the e-mail seriously.

"There is certain factual information in the e-mail. We will be corroborating that to see if that's accurate," Singh told The Associated Press without elaborating.

The e-mail also claimed responsibility for a number of the other bombings that have plagued India over the past three years.

But unlike previous bombings in India, which have targeted Hindu temples, Muslim mosques and crowded local markets, Tuesday's attack had the potential to undermine the country's increasingly lucrative tourist trade.

Jaipur alone welcomed about 1.6 million visitors between 2005 and 2006, raking in nearly US$20 million, according to the latest government statistics available.

"One does worry because news like this flashes around and it does affect people," said Jyotika Kumari, whose family owns the Diggi Palace hotel in Jaipur.

Apart from targeting a tourist center, officials have said they believe the attacks were also intended to stoke tensions between India's Hindu majority and its Muslim minority.

Authorities tried to prevent any retaliatory violence by imposing a daylong curfew for a second day Thursday in Jaipur's walled old city, where the explosions took place.

Since the bombings, Indian authorities have repeatedly suggested blame would eventually fall on Islamic militant groups, many of which India accuses Pakistan of backing.

The attack came days after Indian soldiers came under fire trying to stop militants from crossing the frontier with Pakistan, and after 11 people were killed in fighting between security forces and Islamic militants in the Himalayan region.

Indian authorities say Pakistan-based Islamic extremist groups were behind those incidents and a spate of bombings that have killed hundreds in this predominantly Hindu country of 1.1 billion people since 2005. Pakistan, an overwhelmingly Muslim country, denies any role in the bombings.