It’s being described as a 'private' visit to India for religious purposes. But with less than 48 hours to go for Pakistan President Asif Ali Zardari’s arrival here, on his way to the dargah at Ajmer Sharif, the atmospherics are anything but private as India and Pakistan engage in an exchange of claims and counter-claims over Lashkar-e-Tayyaba founder and 26/11 mastermind Hafiz Saeed.

Amid this exchange came some optimistic remarks from Washington on the forthcoming visit. The US, whose ties with Islamabad have been under considerable strain for many months, said on Friday that the visit is 'very constructive and we’re all for it'.

Striking an optimistic note, US state department spokesman Mark Toner said: “It’s a win-win situation where Pakistan and India are engaging in dialogue, are talking to each other, and are building better cooperation”.

But sparks still flew between the two neighbours. External affairs minister S.M. Krishna fired the first salvo on Friday in Bengaluru, saying India had provided full details on Saeed’s involvement in the Mumbai attacks, and 'no amount of denial would exonerate them'. Pakistan responded by claiming India had not provided any 'concrete evidence'.

This came a day after Islamabad said it was looking forward to a 'constructive engagement' between President Zardari and Prime Minister Manmohan Singh in New Delhi on Sunday.

This exchange came close on the heels of Islamabad saying just a day earlier that it's looking forward to a "constructive engagement" between President Zardari and Prime Minister Manmohan Singh when they meet in New Delhi on Sunday. But there was an important corollary to this too with Islamabad also making it clear that there would be no compromise on the "core issue" of Kashmir or maintaining a credible nuclear deterrence.

Mr Krishna's assertion of India having provided Pakistan with all documentary evidence pointing to Hafiz Saeed's involvement in 26/11 came close on the heels of a similar statement by Union home minister P. Chidambaram. The remarks came after the US put out a bounty of 10 million US dollars for the capture of Saeed earlier this week.

On Friday, Mr Krishna said, "The dossier that the home minister has provided to the Pakistan government contains every detail of Saeed's involvement in the planning and execution of the terrorist attack on Mumbai."

He further said that no denials would exonerate those involved unless there is a judicial enquiry into the entire episode to fix responsibility adding, "unfortunately, the Pakistan government has not thought it proper to investigate this".

Saeed, it is expected will figure in the discussions that Prime Minister Manmohan Singh and president Zardari will have shortly before they sit down for lunch at the former's 7, Race Course Road residence in the Capital. In Pakistan, the US bounty has prompted protests by Islamist right-wing organisations, among them the Jamaat ud Dawa (JuD) which Hafiz Saeed heads. Among other things, they want president Zardari to cancel his India visit.

While New Delhi has been quite tight-lipped about its expectations from the Zardari-Singh meeting while insisting more than once that it's a 'private' visit, Islamabad has been more forthcoming. It has expressed the hope that the April 8 meeting will contribute to regional peace.