Bombay, India ? A powerful explosive favored by Islamic guerrillas in Kashmir was used in the twin bombings in Bombay this week, police said Wednesday, bolstering India’s assertion that Muslim militants carried out the terrorist attack.

At least 51 people were killed and 156 injured in the explosions Monday outside the Gateway of India, a historical landmark, and Zaveri Bazaar, a gold and diamond market.

Police Commissioner Ranjit Sharma said Wednesday that preliminary investigations indicated the explosive RDX was used in both blasts.

“Forensic reports are awaited but we suspect that a small quantity of RDX is responsible for creating this damage,” Sharma told The Associated Press.

Indian security officials say RDX is almost always used by Islamic militants in the Himalayan region of Kashmir, where separatists are fighting Indian forces.

Deputy Prime Minister Lal Krishna Advani on Tuesday blamed the bombings on Lashkar-e-Tayyaba, a pro-Pakistan Kashmiri militant group.

“The use of RDX indicates that this is the handiwork of Islamic militants. We are suspecting Lashkar-e-Tayyaba,” said Sharma.

RDX was last known to have been used in Bombay in March 1993 serial bombings that killed more than 250 people. RDX is a white crystalline solid usually used in mixtures with other explosives, oils, or waxes, and is rarely used alone.

It is a highly lethal military explosive, packing more than 150 percent of the power of TNT. Two pounds of RDX in a bomb can blow up a large commercial aircraft.

The bombs were placed in two taxis that were hired for the day. One of the drivers was killed in the blast but the other driver escaped as he was strolling outside after parking in front of the Gateway of India.

Police are looking for five suspects, including two women who hired the taxi that went to the gateway.