Distrust between India and Pakistan and a "hawkish" Indian mindset were complicating efforts to resolve disputes over the water of shared rivers, Pakistan's top river water official said.
Some analysts fear that disputes over water between the old rivals could in future spark conflict as the neighbours compete for dwindling supplies of water from melting Himalayan glaciers.
The foreign secretaries of India and Pakistan, which have fought three wars since 1947, will meet in New Delhi on Thursday marking the resumption of official contacts which India broke off after militants attacked the Indian city of Mumbai in late 2008.
Pakistan wants to put the dispute over river waters at the top of the agenda along with the core dispute over the divided Kashmir region
But Indian Foreign Secretary Nirupama Rao said on Monday that Indian concerns about militant groups based in Pakistan would form the main focus of the talks with her Pakistani counterpart.
"There's mistrust and a lack of confidence," Syed Jamaat Ali Shah, the Indus Water commissioner of Pakistan, told Reuters in an interview on Tuesday.
"There has been reluctance to share information about the water situation in the rivers, which is sad," he said.
The use of the water flowing down rivers which rise in the Indian part of Kashmir and flow into the Indus river basin in Pakistan is governed by the 1960 Indus Water Treaty.
Under the accord, India has the use of water from three rivers in the east - the Sutlej, Beas, and Ravi.
Pakistan was awarded use of the waters of the western rivers - the Indus, Chenab and Jhelum.
But Pakistan accuses India of violating the treaty by reducing the flow of water down the rivers it was awared use of.
In particular, Pakistan objects to two planned Indian projects, the Wullar barrage, as it is known in Pakistan, or the
Tulbul navigation project, as India calls it, and the Kishan-Ganga hydroelectric and water-diversion project.
Shah said the barrage would reduce water flow in the Jhelum river. The water diversion planned in the Kishan-Ganga dam, on a tributary that flows into the Jhelum, would have a serious impact on the Pakistani side and it would seek international arbitration if the dispute could not be resolved bilaterally, he said.
Pakistan also objects to India's Baglihar hydro-power and water storage project on the Chenab river.
But water is also a divisive issue within Pakistan with the downstream southern provinces of Sindh and Baluchistan complaining that upstream provinces, in particular Punjab, take more than their fair share.
Indian denies any unfair diversion of Pakistan's water.
Some Indian analysts say Pakistani complaints are aimed at diverting attention within Pakistan from the internal water row.
Indian officials also say Pakistan is raising the issue to counter India's attempts to keep the focus of Thursday's talks on militancy.
"Raising the water issue appears to be a diversionary tactic," said an Indian official who declined to be identified.
But Shah played down analysts' fears of conflict over water.
"I don't think the water dispute would become a flash-point," he said. "We want India to get its rights but it should also fulfil its obligations."
If disputes were handled properly, according to a mechanism set out in the 1960 treaty, the exploitation of the water could be a factor for cooperation, he said.
"It could be a foundation for good relations between the two countries," he said.