US Treasury Secretary Janet Yellen has said she is confident that EU holdouts, including Ireland, who oppose a global tax reform would find a way to accept the deal.

Yellen said she made her arguments backing the OECD deal in talks with ministers from Ireland and Estonia, two of the countries that have yet to accept a plan that has been approved by 132 countries.

Meeting in Venice on Saturday, G20 ministers, including Yellen, endorsed the plan to overhaul the way multinational companies, including US digital giants, are taxed.

"My message is that this is an agreement that is historic... and it's important that everyone try to get on board," Yellen told reporters in Brussels.

"Obviously that involves compromises and my sense is that those countries want to find a way to get to 'yes'," she said after her meetings with the holdouts.

Among other officials, Yellen met with Minister for Finance, Paschal Donohoe, whose buy-in will be crucial for the EU to approve the deal for a 15%-plus global minimum corporate tax.

"He's head of the Eurogroup of (euro zone) finance ministers, he invited me to meet with them. Clearly he has a strong interest in the success of the EU," Yellen said.

Yellen said she also spoke with the president and finance minister of Estonia, another EU country that has not signed up.

She said Ireland might have to raise its 12.5% corporate tax rate a bit, but would remain competitive globally given advantages such its well-educated workforce and excellent business environment.

Yellen added that she was "pleased" by a decision by the EU to delay its plan for a European digital tax in an effort to not jeopardise the global deal.

The former central banker said the EU tax, which was supposed to be announced this month, would have come at a "delicate time", when she is gathering support for the OECD plan in Washington.

"I think it avoids throwing something into the negotiations that would be unclear and could complicate our progress," she said.

The world's 20 largest economies endorsed on Saturday a plan for a global overhaul of corporate tax that would introduce a minimum tax rate and change the way large companies like Amazon and Google are taxed, based partly on where they sell their products and services rather than on the location of their headquarters.

The reform, if finalised in October, would need parliamentary approval in the more than 130 countries that support it, including the US Congress where it could face opposition from the Republicans.

All EU member states must also approve tax reforms, including the envisioned global deal.