Expressing concern over increase in infiltration attempts, Prime Minister Manmohan Singh on Sunday said the centre and the states should launch coordinated efforts to tackle internal security threats.

Addressing the Chief Ministers' Conference on Internal Security here, the prime minister said hostile groups and elements operate from across the border to perpetrate terrorism and Jammu and Kashmir faces the brunt of this.

Identifying left-wing extremism, cross-border terrorism and insurgency, besides attempts to flare up communal tension as challenges for internal security, he said the states and the centre should work together to tackle such threats.

Singh said fake Indian currency notes (FICN) are being printed and smuggled from across the border which need to be tackled with coordinated efforts and recommended the states to set up nodal agencies for investigating seizure of counterfeit currency.

The prime minister also reaffirmed his earlier stand that left-wing extremism remains the gravest threat to internal security.

Earlier, Home Minister P. Chidamabaram made a strong pitch for strengthening state police forces, especially the intelligence cells and specialised units, to tackle any terror threat.