As investigators try hard to find clues, Union Home Secretary RK Singh on Tuesday said there was no evidence till now to suggest involvement of any country in the bomb attack on an Israeli diplomat in Delhi.

"We have no evidence to name any country. It's premature to take any country's name," he told reporters when asked whether there was Iranian hand in yesterday's terror attack which left four persons including an Israeli diplomat injured.

The home secretary said the investigators were yet to zero in on people behind the crime and no material has suggested involvement of any particular country.

"We don't have any idea who planted it. There is no material to show involvement of any country. The perpetrators behind the attack will be known only after the investigation is completed," he said.

Meanwhile, official sources said there was no prior intelligence input about yesterday's terror strike and the device used to carry out the blast was very sophisticated and it was used in India for the first time.

After examination of the blast site, forensic experts have concluded that neither any battery nor any circuit was used in the bomb but traces of aluminium were found from the spot. The experts also said that RDX was also not used in the explosion.

Meanwhile, the Home Ministry has issued an advisory to all states to beef up security in Jewish establishments and for Israeli tourists visiting India.

The Centre also told the states hosting diplomatic missions of Israel, the United States and other Western countries, to beef up security there. The Home Ministry also advised the states not to allow parking near any missions and make alternative arrangements for it.