Seven people, including a married couple, were detained today as Indian police searched for the bombers of the Friendship Express train, which was attacked on its way to Pakistan on Sunday night with the loss of 68 lives, according to Indian reports.

The suspects were held after raids in New Delhi and the three states of Rajasthan, Punjab, and Uttar Pradesh, police said.

“Interrogation in the case is on the right track,” said Rajiv Dalal, the chief of police in Haryana, where the attack took place. Mr Dalal said that some of the people were picked up in Bikaner, a town in northern Rajasthan near the border with Pakistan.

The Times of India reported this evening that a husband and wife were detained in Bikaner and had been brought to Jaipur, the capital of Rajasthan, for questioning. The man resembles one of the sketches released by police on Tuesday, the newspaper said.

The images were constructed from witness descriptions of two men seen leaving the train shortly before two crude, kerosene-fuelled devices exploded on the Samjhauta (Friendship) Express which runs from New Delhi to Lahore in Pakistan. So far, relatives of the dead have only been able to identify 33 of the 68 burned corpses.

As the investigation fanned out across India, investigators revealed several possible lines of inquiry and scrutiny turned towards Islamic extremist groups that oppose the peace process between India and Pakistan and of which the train that joins the two countries is a popular symbol.

Investigators in New Delhi told Reuters that two other bombs left on the train failed to explode and had left potentially valuable forensic evidence. For instance, one of the devices was wrapped in a Hindi newspaper from Aligarh, a town with a large Muslim population in Uttar Pradesh, police said.

A Pakistani man, Usman Mohammed, who had thrown one of the suitcase bombs off the train and had been held for questioning, was released today.

Meawhile, R.C Mishra, a senior officer in the Haryana police team, said that investigators were trying to track down several people who boarded the train in Delhi heading for Pakistan but never arrived and were not found among the dead either. Of the 33 victims identified, 27 were Pakistanis and 6 were Indian.

Indian newspapers reported that police were also investigating a suspicious phone call made to Pakistani Kashmir just after the bombs exploded, suggesting a connection between the attack and Kashmiri separatist groups, including Lashkar-e-Taiba, the largest and most-feared militant organisation.

Sunday's atrocity immediately preceded a visit by the Pakistani Foreign Minister, Khurshid Kasuri, and scheduled talks with the Indian Government, which have continued as planned. The two countries insist they are collaborating in the bombing investigation, with a new joint anti-terrorism panel due to meet on March 6.

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