Before the CBI, the Kerala government had also consulted the Indian Army about the mines.

Highlights 5 Claymore mines, exclusively used by Army, were found last year

Kerala Police had registered a case on the same day to probe the matter

Last month, centre ordered CBI probe into how mines reached Kuttipuram

The Central Bureau of Investigation has launched an investigation into five Claymore mines, exclusively used by the Indian Army, that were found under Kerala's Malappuram district in January last year. The mines were discovered under the Kuttipuram bridge, triggering an alarm.

The Kerala Police had registered a case on the same day to investigate the matter but sensing the seriousness of the subject and also as it involved national security, the Kerala government had formally recommended a CBI probe in October.

Processing the request, the centre last month ordered a CBI investigation to probe how the mines reached the Kuttipuram riverbed.

"After receiving the notification from DoPT for a detailed investigation into the said matter, agency has got relevant case related documents from the Kerala Police and the case has been handed over to the Special Crime Branch of the Thiruvananthapuram unit of the CBI," a senior official of the CBI told NDTV, requesting anonymity.

The senior official also added "the said military grade mines were recovered under the Kuttippuram bridge on NH-66 which is usually used by Sabarimala pilgrims from Karnataka, Andhra Pradesh and northern districts of Kerala... all possible angles are being looked into."

A copy of the FIR seen by NDTV said that a Kerala police office received a phone call on January 5, 208 about "suspicious substances" seen under the Kuttipuram bridge.

"On reaching the spot, [he] found five numbers of semi concave shaped metal substances in same sizes and two other metal pieces along with five bags. As per the direction, bomb detection and disposal squad was called in for examination and the said materials were seized," the FIR said.

Before recommending a CBI probe, Kerala Police had also sought the assistance of the Indian Army and based on their inputs, the state government decided to hand over the case to the CBI, sources have told NDTV.