Police in India's western city of Mumbai have arrested two more suspects in connection with bomb blasts on 11 July which killed more than 180 people.
Police say the suspects belong to the Simi group
Those arrested on Tuesday were named as Jameel Ahmed and Suhail Shaikh.
One was arrested from Mumbai and the other from the nearby city of Pune. The total number of people formally arrested has now risen to six.
Police sources said all those so far arrested were part of a team which conspired to detonate the bombs.
They say that the suspects have been linked to a banned organisation, the Students Islamic Movement of India (Simi), which police said, was taking instructions from the Pakistan-based militant group, Lashkar-e-Toiba.
The BBC's Zubair Ahmed in Mumbai says that police in the Anti-Terrorism Squad have been questioning the men for the last few days, but the arrests were formally made on Tuesday.
Security has been stepped up on the India-Bangladesh border
Our correspondent says that the squad has also detained a number of other people and is on the look out for at least a dozen more.
Those still being sought are all alleged to be Tanveer Ahmed Ansari's accomplices.
Mr Ansari - who practised traditional Indian medicine in Mumbai - was arrested on Sunday night.
Police say the latest arrests mean they are now close to solving the case, but correspondents say that traditionally police in India overstate their progress when investigating major cases of public concern.
Meanwhile India has announced that it is stepping up security on its borders with Nepal and Bangladesh after investigations into the bombings showed that militants and weapons were smuggled from those areas.
Officials told the Reuters news agency that the number of border guards on the open frontier with Nepal would be doubled to nearly 11,000.
They say that troops have also been ordered to speed up the construction of a security fence on the border with Bangladesh, and use high-technology equipment to monitor the area.
"It is an open border with Nepal and anybody can enter anytime and we are viewing this seriously," Inspector-General of police Raj Kanojia told Reuters.
"With penetration impossible from the northern side due to strong presence of army and police, the militants are using the eastern side to infiltrate," he said.