A powerful explosive favored by Islamic guerrillas in Kashmir (searchwas used in the twin bombings in Bombay (search) 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 (search), 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 the 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.

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

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.

On Wednesday, about 1,000 Hindu nationalists marched silently from Gateway of India, where one of Monday's bombs was detonated, to offer their sympathy for the dead.

The marchers belonged to the Hindu nationalist Bharatiya Janata Party of Prime Minister Atal Bihari Vajpayee, and its ally, the even more nationalistic Shiv Sena,

"We won't shout any slogans. It is a silent march. We want to pay homage to the victims of the bomb blast, both Hindus and Muslims," said Rajiv Kori, a member of the Shiv Sena.

It was an unusual show of unity by the Shiv Sena, a group better known for its disdain of India's minority Muslims.

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.

On Tuesday, Advani stopped short of saying that Pakistan had sent the bombers, but accused it of sponsoring terrorism since 1971.

The comments were likely to undermine a fragile peace process between the two nuclear-armed neighbors. They have fought three wars, two over the divided Kashmir province.

The other recent explosions in Bombay have been blamed on Lashkar-e-Tayyaba group and its ally, the Students' Islamic Movement of India.

Pakistan, which banned Lashkar-e-Tayyaba last year, has condemned this week's bombing and rejected Advani's accusations.

Information Minister Sheikh Rashid Ahmed said Advani "often levels baseless allegations against Pakistan."

"Pakistan has never supported terrorism in India," he said.

Relations between India and Pakistan have been improving in recent months. A peace process was back on track after being broken off when the two nations nearly went to war over an attack on the Indian Parliament in late 2001. Since then, diplomatic ties have been restored, buses are crossing the border and officials are talking about resuming air links.