A doctor has been arrested in connection with the deadly wave of terror attacks that rocked Mumbai on July 11, taking the total number of arrests to four.

Tanvir Ansari, an alleged Lashkar-e-Tayiba operative who practices Unani medicine in central Mumbai, was arrested on Sunday night, Anti-Terrorism Squad sources said on Monday.

He was arrested by Crime Branch and later handed over to the ATS, they said. He will be produced before a local court later in the day.

"Ansari had undergone training in Pakistan in handling arms, ammunition and making bombs and explosives. He is suspected to have provided such training to others," they said.

Earlier on July 21, police arrested three persons for their alleged involvement in the serial blasts in Mumbai suburban trains that claimed about 200 lives and injured over 700.

Two persons -- Kamal Ahmed Mohammad Vakil Ansari and Khalid Aziz Raunaq Aziz Sheikh -- were arrested from Bihar while the third -- Mumtaz Ahmed Maqbul Ahmed Choudury � was nabbed from Navi Mumbai. They were remanded to 10-day custody.