New Delhi, June 22 (IANS) The explanation given by the Intelligence Bureau (IB) that the adhesives found in Finance Minister Pranab Mukherjee's office were chewing gums, is a "joke", the Bharatiya Janata Party (BJP) said Wednesday.

"IB's chewing gum theory is a joke. A childish argument like this...if they want the country to believe that it was a chewing gum, people will laugh," BJP leader Sushma Swaraj told reporters Wednesday.

"From where such intelligent chewing gum came, which goes to the finance minister's room, his OSD's room, advisor's room, to the conference hall, and sticks? Before giving such argument, the IB must think," she said.

According a newspaper report, Pranab Mukherjee wrote to Prime Minister Manmohan Singh in September last year, asking him to order a "secret inquiry" after some adhesives were found planted in his office and in some other areas in the finance ministry's North Block office.

"There are two questions in this incident - whether the spying was being done by the government itself or some corporate house was getting it done," Swaraj said.

"In both situations, the matter is serious. If the government was doing this, it is an example of the growing mistrust between the ministers in the government. And if it was being done by a corporate house, it is a big lapse in security cordon," she said.

The leader of opposition also compared the incident to the Watergate scandal in the US.

"Both ways, the probe is very important, that is why I called it Watergate yesterday, because in similar incident, the American president had to resign even though it was against the opposition. Here, the spying is against its own finance minister," she said.

She also said that the finance minister must know the difference between a chewing gum and an adhesive.

"The chewing gum theory being presented to the nation is not right. I request the government the letter he had written should be taken seriously, and to do a through investigation," she said.

Pranab Mukherjee Tuesday said that the IB probed a possible security breach in his office but found nothing.

According to the report, the Central Board of Direct Taxes (CBDT), which has also its office in the premises, engaged a private detective team, which found adhesive at three locations along the edge of Mukherjee's table. Grooves were found on the surface which could have been the imprint of a possible device, the report said.

However, the IB downplayed the incident and said the adhesive was a "sort of chewing gum", the report added.