The latest arrests take the number of people in police custody to six in an investigation that has straddled several Indian states as well as neighbouring Nepal and Bangladesh.

Police have raided slums and Muslim quarters across India, and questioned hundreds of people, mostly Muslims, but most have been allowed to go.

KP Raghuvanshi, chief of Mumbai Police's anti-terrorism squad, said: "Two men were arrested yesterday [Tuesday] night for their role in the blast incidents."

Police suspect that the men gave logistical support to the bombers.

They are to appear in court in Mumbai on Wednesday. The charges against them were not immediately known.

Tanvir Ansari, a doctor of traditional Indian medicine, was arrested in connection with the case this week. Police said he had gone to Pakistan in 2004 to train in the use of weapons and bomb-making.

Investigators say Lashkar-e-Taiba, an Islamist militant group based in Pakistan, and a Pakistani military spy agency may have planned the attacks.

Islamabad has said such allegations are unsubstantiated and offered New Delhi help in the investigations, which India has turned down.