"The two men were wearing helmets and raincoats. They fired indiscriminately at a tourist bus before escaping," K. Singh, a senior police officer in Delhi, told Reuters.

Six Taiwanese nationals were boarding the bus on a visit to Jama Masjid when the shooting happened, the vehicle's driver said. The historic mosque in the old, congested part of the capital is one of Delhi's most popular tourist attractions.

Police said they detained a young man who owned the motorcycle used in the shooting. He lives in the Vasant Kunj area of south Delhi.

An e-mail purportedly from the Indian Mujahideen, a homegrown militant group, was sent to the BBC just after the attack. The statement threatened attacks on the Games and criticized India for alleged oppression in Kashmir.

"We know preparations for the games are at its peak. Beware we too are preparing in full swing for a great surprise," said the e-mail, published on the BBC Hindi service website.

Security has been tightened in the capital before the Games, with authorities mindful of militant attacks in Indian cities over recent years in which dozens have been killed.

Police would not confirm whether militants were behind the latest attack. "There was some firing outside Gate No. 3 of Jama Masjid," Delhi police spokesman Rajan Bhagat said. "We can't say whether it was a militant attack. We suspect it is a disgruntled gang of criminals who planned this attack basically to discredit the Delhi police."

"The claim sent to various media outlets is not reliable because the attack was carried out in a very unprofessional and crude manner, which no organized terrorist group would do," a senior policeman said, requesting anonymity.

Doctors said the condition of the two wounded foreigners was stable and one of them was undergoing surgery.

Taiwan Foreign Ministry spokesman James Chang said one of the tourists had suffered a grazed head and the other was wounded in the abdomen. Neither wound was life-threatening.

The Commonwealth Games, an event organized by the 54-member organization of mainly former British colonies and held every four years, begin Oct. 3. But the Games threaten to become an embarrassment with the organizers fighting corruption charges and struggling to get venues ready on time. The cost of the event has risen more than 17.5 times from the original estimate and is now put at $6 billion.

"All that I can appeal to everybody is, please do not panic. An incident like this is something worrying but nothing to panic about," said Shiela Dikshit, Delhi’s chief minister.

The Commonwealth Games organizers said the Games would go ahead as planned in a "safe and secure environment."

"The shooting incident this morning in Delhi will have no impact on the Commonwealth Games," organizing committee Secretary-General Lalit Bhanot said in a statement.

"The Ministry of Home Affairs and Delhi police have made elaborate arrangements to provide the Commonwealth Games athletes and officials a safe and secure environment."

In 2006, at least seven people were injured when two blasts rocked the same area.

There have been militant attacks in India this year. In February, an explosion ripped through a restaurant in the western city of Pune, killing 17 people. The government blamed that attack on Indian Mujahideen.

India is constantly on guard against attacks from terrorist groups, particularly the Pakistan-based Lashkar-e-Taiba, which New Delhi blamed for the Mumbai 2008 atrocities and a 2002 attack on the national Parliament.

Home Minister P. Chidambaram warned last month, however, that Hindu extremists posed an increasing risk to national security, dubbing the threat "saffron terror".