The amount of soured loans the Dublin banks advanced to property developers in Belfast which will be transferred into the National Asset Management Agency (Nama), is much less than earlier estimates communications minister Eamon Ryan gave in the Dáil, senior industry sources say.

Ryan said in April he believed about 15% of the distressed loans Nama planned to buy would come from Northern Ireland. This led to some suggestions that the Northern Irish loans could be worth as much as €13bn.

The minister's comments led to unionist leaders in the North sounding an alarm about potential fire sales depressing the North's fragile property markets.

The three Dublin banks, AIB's First Trust, Bank of Ireland and Anglo Irish, loaned substantial amounts across the North for commercial-property developments. Other private syndicates through stockbrokers also borrowed monies to purchase residential-property sites in the Belfast suburbs.

But sources in Dublin and Belfast say that the amounts involved were much smaller than popularly believed because Northern land prices, though rising rapidly in the recent boom years, were starting from low levels because of the long-depressed nature of the economy in the North.

"I think 10% looks high to me. Even €8bn of loans [going into Nama] from the North looks high to me," a senior source said.

The North's First Minister, Peter Robinson, last month said that he feared the "potentially damaging effect on the property market" if the Dublin banks were forced to offload their Northern assets in any fire sales. That "would depress the value of property still further", the DUP leader said.

"I raised this issue with Brian Cowen at the North-South ministerial meeting and he agreed that it was important that we agreed a way forward to ensure that there was a co-ordinated response to tackling the disposal of assets.

"I then agreed with the Republic's finance minister Brian Lenihan that he and our finance minister Sammy Wilson would meet to discuss how to take this issue forward in a way that does no damage in either jurisdiction," Robinson said.