Finance Minister Paschal Donohoe has said he believes September and October will be the key period for agreeing international tax reforms.

Addressing the American Chamber of Commerce Ireland Global Conference, he reiterated his concerns over a global corporate minimum tax rate.

Mr Donohoe said he had reservations about a "high" minimum tax rate on the basis that it could be a step towards global tax harmonisation rather than addressing aggressive tax planning.

He added that small countries such as Ireland needed to be able to use tax policy as a legitimate policy tool.

"I think the period September to October will be a particularly important period in laying out what kind of change is in prospect for years to come," the minister said.

Mr Donohoe acknowledged that the cost to the Exchequer of any new proposals would amount to around a fifth of our corporate tax revenues.

The total tax take under that heading reached €11.8 billion last year.

He said he recognised that reframing the international tax rules for the modern age was an important step towards contributing to certainty and stability globally.

"There are risks in an agreement, but the risks may be greater with continued uncertainty and instability if there is no agreement," the minister said.

Meanwhile, France, Germany and Italy have said new US proposals for a global minimum corporate tax rate of at least 15% formed a good basis for sealing an international deal by July.

The US Treasury Department offered last night to accept a minimum rate of at least 15%, significantly below its proposed 21% minimum for US multinational firms.

It made the proposal at the Paris-based Organization for Economic Cooperation and Development (OECD) where nearly 140 countries aim to reach broad agreement this summer to rework rules for taxing multinational groups and big technology companies, such as Alphabet and Facebook.

"Treasury proposed to the steering group that the global minimum tax rate should be at least 15%," the department said in a statement. "Treasury underscored that 15% is a floor and that discussions should continue to be ambitious and push that rate higher."

US Treasury Secretary Janet Yellen first proposed a 21% US corporate minimum tax in April as part of President Joe Biden's $2.2 trillion infrastructure spending proposal, which would be financed largely by increasing the US corporate tax rate to 28%.