Claiming 'vital' leads in the serial blasts that left 21 dead, Delhi [Images] Police has detained six suspects amid clear indications of a similarity with the Ahmedabad [Images] blasts in July for which SIMI [Images] has been suspected.

 Images: Shock and horror in Delhi

Sources in the investigation agencies said that two people have been picked from the walled city and two more from Okhla. The suspects, believed to have links with banned SIMI outfit, were being questioned by joint teams of central security agencies and police.

While two more were also being quizzed, two others detained from Barakhamba Road have been released, they said.

The hunt for the Indian Mujahideen's 'al-Arbi'

Delhi Police spokesman Rajan Bhagat said 'we have got vital leads' but declined to give details saying 'we will solve the case soon'.

Initial probe pointed to a group belonging to Western Uttar Pradesh [Images] behind the five coordinated blasts at Gaffar Market in Karol Bagh, Connaught Place and Greater Kailash.

View: Pathetic handling of blasts' aftermath

Police teams have been sent to neighbouring UP and Rajasthan.

They said the role of Mumbai-resident Mohammed Subhan Quereshi, suspected SIMI activist, was being probed. Police believe that he could have hacked the WiFI system in Mumbai to send the terror e-mail to various media houses.

Strong similarities were found between the Delhi blasts and the serial explosions in Ahmedabad on July 26 that left 53 dead. Indian Mujahideen [Images], a shadow amalgam of banned SIMI and Lashker-e-Tayiba, claimed responsibility for the blasts through an e-mail sent to news organisations around the same time when the explosions occurred.

SIMI's Hubli meeting was key

Sketches of suspected bombers were being drawn by the Delhi Police with the help of five eye-witnesses, including a teenage balloon seller, who claimed to have seen them placing packets in the dustbins at Central Park in Connaught Place.

Forensic experts and security agencies were trying to piece together the remnants of the explosives at the blasts sites in all the five places.

About one and a half KG of Ammonium Nitrate, which has become easily available explosive material for terror modules, and steel balls were used in each of the bombs which were synchronised with an Integrated Circuit and an alarm clock.

Twelve-year old Rahul, a father-son duo who sell fried items at Barakhamba Road, were among those summoned to the police headquarters.

Rahul claimed he saw two bearded men in pyjama-kurta place a packet inside a dustbin. The boy said they quickly left in a three-wheeler minutes before the blast.

Prime Minister Manmohan Singh [Images] visited Ram Manohar Lohia hospital and enquired about the health of the injured.

Union Home Minister Shivraj Patil [Images] chaired a high-level meeting to assess the security situation.  After the 90-minute meeting, Home Secretary Madhukar Gupta told media persons, "We have discussed various measures that may be needed not only in Delhi but other major cities."

With the festive season of Eid and Dusherra approaching, the security agencies are keeping their fingers crossed as the militants, in their terror mail, have threatened more attacks in other major cities.

Keen to get back to their normal life, people were seen by afternoon out in markets in most parts of the capital but an uneasy calm prevailed in the blast-hit Karol Bagh and Connaught Place areas.

Relatives thronged several of the city hospitals where the victims were being treated.