Devi Asmarani, Jakarta – The Indonesian police said yesterday they were having difficulties finding proof to link the series of bomb attacks in the capital in the past three months to groups that some government officials suggest are related to the army.

A top source in the national police headquarters said the police had not been able to substantiate the role of Indonesian military (TNI) elements in the bombings, the most recent of which occurred on Wednesday. But he admitted that all the four incidents in the past months were related and done by "highly skilful people" to cripple the economy and further destabilise the country.

"Is the military involved in the bombing? Yes and no," the source told The Straits Times. "After narrowing the list of those who could be behind the bombings, we have our suspicions. But we don't have the proof and without it, we cannot touch the TNI headquarters. These are still assumptions that must be checked, and this will include scrutinising the TNI, but it will be difficult because the TNI is a closed institution."

The government has implied that some rogue military elements might be behind the campaign of terror to undermine its legitimacy, and that there have been efforts to block the police investigations.

"The government feels that clearly there have been obstacles in the sense that police investigations had been discontinued when they were about to conclude that the military apparatus might be involved – they are beyond the reach of the police," Attorney-General Marzuki Darusman said on Thursday. "TNI chief has been authorised to break through this barrier and to resolve the problem institutionally," he said.

Yesterday, Mr Marzuki told The Straits Times that he was airing public suspicions of military involvement to prod the police into expediting its probe. "If it is not the case that police investigations are held up because of military obstruction, then the police should come up with a public denial and get on with investigations in a different direction. I am willing to retract my statements if it is not the case that the military is obstructing them," he said.

Police have yet to name any suspects. In a recent interview, former Defence Minster Juwono Sudarsono linked the bombings and the spate of violence across the country to the "residual financial power" of Suharto and his former TNI commander General Wiranto, who was sacked by President Abdurrahman Wahid early this year.

"The liquidity of their power is more than the formal logistics of the military," he said, adding, that the group also benefited from the ineffective leadership of TNI chief Admiral Widodo.