Bengaluru, Feb 17 (PTI): Investigators have zeroed in on some terror groups in connection with the explosion outside a restaurant here that killed a woman and injured three others in December last year, city police said.

"At this stage, we can say that we have specific doubts and suspicion on one or two groups; we have our teams which are investigating on them, the contacts they have, the network they have," City Police Chief M N Reddi told reporters here. ` He said these are "sleeper cells not based in but outside, we are collecting information on them and network behind them."

A woman was killed and three others injured in the blast triggered by an Improvised Explosive Device (IED) in front of a popular restaurant on a busy road in the heart of the city on December 28.

The IED wrapped in a plastic bag and placed in a bushy plant went off around 8.30 PM on the fateful night in front of Coconut Grove restaurant, killing the woman in her 30s.

Stating that Special Investigation Team (SIT) is probing the case, Reddi said "the case is being reviewed by the officials at the senior level; I'm also reviewing it constantly."

He said there is no "specific development in the case so far. No specific individual reference can be made till now," he added.