Indian police have stepped up security in major cities as they hunt down those responsible for Monday's twin car bombs in Bombay that killed at least 46 people and injured close to 150 others. India is still reeling from the shock of the massive explosion that shook the country's commercial capital.

Funerals have been held for some of the victims and clean up operations continue at the two bombing sites - a crowded jewelry market and Bombay's most famous landmark, the Gateway of India.

Tuesday morning most of the city had returned to normal with shops, schools and businesses open. However, some shops in the jewelry market where one bomb went off were closed, and the area around the Gateway of India was cordoned off.

No one has claimed responsibility for the attacks and police say they have no direct evidence yet of who may have been behind the bombings.

They reportedly are looking into possible links to two Islamic groups - the banned Islamic Students Movement of India and the Pakistan-based Lashkar-e-Taiba, one of a number of militant groups fighting Indian forces in the disputed area of Kashmir.

In the past, India has quickly blamed neighboring Pakistan for being behind such attacks, a charge Islamabad has repeatedly denied.

This time, Bombay Police Commissioner Ranjit Sharma implicated what he termed "the enemy nation," an apparent reference to Pakistan. But, senior government officials have refrained from such finger pointing. Pakistan has condemned Monday's bombings.

Almost immediately after the bomb attacks in Bombay, Indian police stepped up security in major cities across the country, especially around religious sites. Bombay has suffered a series of bombings in recent months, most targeting the city's crowded public transportation system. The attacks have generally been blamed on Islamic militants.

There is a good deal of speculation about the motives for Monday's bombings and many Bombay residents are quoted as saying the attacks were designed to heighten tensions between Hindus and the country's Muslim minority. They point out, however that both Hindus and Muslims were among the victims of Monday's bombings.