The government's Anti-Terror Squad released photos of two young, bearded men it identified as Sayyad Zabiuddin and Zulfeqar Fayyaz. Their nationalities were not provided.
It also was not clear where the photos, headshots which appeared to have been taken for identification documents, originated.
Police earlier detained about 350 people for questioning amid suspicion that Kashmiri militants could be linked to Tuesday's bombings.
The detentions came as a man claiming to represent al Qaeda said the terror network had set up a wing in Kashmir and praised the attacks.
A senior intelligence official said the government was taking the claim seriously and authorities were trying to trace a call the man made to a Kashmiri news service.
"Our immediate effort is to locate the caller and ascertain the authenticity of the claim," the official said on condition of anonymity because he was not authorized to speak to the media. "The government is taking it very seriously."
There have been allegations that Islamic militants fighting to wrest predominantly Muslim Kashmir from India have ties to al Qaeda, but Thursday's statement would be the first time Osama bin Laden's network claimed to have spread to Indian territory.
CBS News' Ranjan Gupta says (audio) "to the average Indian it seems that these people are trained in Pakistan and Afghanistan, cross over the borders into Kashmir and from there it's very easy to move around in a highly populated country like India."
Police Inspector S. Goshal said most of the 350 detentions were made overnight in Malwani, a northeastern suburb of Bombay. They were rounded up only for questioning to help with the investigations, and none have been charged or formally arrested, he said.
Bombay police Commissioner A.N. Roy said those rounded up included known thugs, gangsters and troublemakers who might have information about the culprits.
Investigators were looking into a possible link with Lashkar-e-Tayyaba, an Islamic militant group based in Kashmir, said P.S. Pasricha, police chief of Maharashtra state. Lashkar has in the past employed near-simultaneous explosions to attack Indian cities.
A spokesman for Lashkar, Abdullah Ghaznavi, denied the group was involved.
The purported al Qaeda member, who identified himself as Abu al-Hadeed, appealed to Indian Muslims to take up jihad and said "whosoever has carried out the attacks in Bombay we express our gratitude and happiness." It was impossible to verify his identity or his claims independently.
The train bombings "are a reaction to what is happening to the minorities, especially Muslims in India," the man said in a statement read over the phone to Kashmir's Current News Service.
"We appeal to Muslims in India to fight for freedom and Islam and choose jihad as their way to achieve freedom and establishing Islamic ways," he was quoted as saying.
The Current News Service said the man spoke in Urdu, the language of most Muslims in the Indian subcontinent, though he identified himself with an Arabic name.
"Today a unit of al Qaeda has been established in Jammu and Kashmir which shall henceforth be called al Qaeda Jammu and Kashmir," the man said. "We shall be giving out statements regularly and will soon announce our aims and objectives."
The government, meanwhile, reiterated its commitment to fight terrorism.
"Nothing will deter us from our firm policy to fight this menace till it is wiped out. We are determined to apprehend and bring to justice all those responsible for the evil acts in Mumbai," said a Cabinet statement. Bombay is also known as Mumbai.
The Indian Foreign Ministry demanded Wednesday that neighboring Pakistan dismantle all terrorist networks on land it controls — but fell short of directly accusing it for the attacks.
Kashmir is divided between the two countries but claimed by both. The region is largely Muslim, and the militants want a Kashmir independent of Hindu-majority India or joined to Pakistan.
"I think this is much more likely to be a geographically confined conflict than something that really threatens the West," CBS News terrorism analyst Christopher Whitcomb, a former FBI agent, said.
In an interview with The Associated Press in Washington, Pakistan's foreign minister bristled at suggestions that his country bore responsibility for the attacks.
"You can't really blame everything on Pakistan; it's very unfair," Khurshid Kasuri said. "India is a vast country. There are lots of people who have their own agendas, not just in Kashmir."
Bombay, a city of 16 million people, was back on track Thursday with tens of thousands of people jamming the commuter train service that was hit by eight bombs, killing at least 200 people and wounding 700.
"The city has faced attacks in the past. It has always bounced back quickly ... people have to go to work. What else are we going to do," said Ashwini Lolo, an office worker in his 20s, at the Bandra station waiting to board a train.