As investigators struggled for a breakthrough eight days after the twin blasts, two suspected Indian Mujahideen(IM) operatives, who had allegedly recced the area of the attack, were brought here from Delhi's Tihar jail today and grilled by NIA sleuths.

No arrests have been made in connection with the terror attack on February 21 in which two powerful Improvised Explosive Devices(IED) went off in the crowded Dilsukhnagar area, leaving 16 dead and injuring 117.

Syed Maqbool and Imran Khan, currently lodged in Tihar Jail following their arrest by Delhi Police in the 2012 Pune blasts, were brought to Hyderabad after a Delhi court yesterday granted the National Investigation Agency(NIA) five-day custody of the two men for interrogation.

The NIA had told the court it would take the two men to Hyderabad and question them for more clues about the blasts, as the ongoing probe pointed to the banned Indian IM module being behind it.

The NIA had alleged that Maqbool and Khan had in July last year recced the Dilsukhnagar area.

"The duo are in NIA custody and are being questioned here," sources said without elaborating.

According to the NIA, the blasts took place on the alleged instructions of IM's Pakistan-based founder Riyaz Bhatkal and the duo's interrogation will help in unearthing the exact plan plotted by him.

The blasts were triggered by the IEDs planted near Konark and Venkatadiri theatres in Dilsukhnagar.

Andhra Pradesh DGP V Dinesh Reddy yesterday said sketches of suspects were being prepared, and he was hoping for a breakthrough.

"There are a lot of eye-witnesses and with inputs provided by those injured in the blasts we are trying to prepare the sketches of suspects, which will be released shortly," he said, adding, investigators were working on some clues.

The DGP had said police have "very valuable data available" and "it is a matter of time we will get a breakthrough".

"We are making rapid stride of progress and I am happy the way the investigation is going on," he said.

The state government has formed 15 probe teams besides the NIA which is also probing the case.