US President Donald Trump complained Tuesday that possible euro stimulus measures floated by the head of the European Central Bank make it "unfairly easier" for the EU to compete against the United States.

Comparing EU policies to those of China, which Trump has engaged in a major trade war, the US president criticised ECB chief Mario Draghi.

"Mario Draghi just announced more stimulus could come, which immediately dropped the Euro against the Dollar, making it unfairly easier for them to compete against the USA. They have been getting away with this for years, along with China and others," Trump tweeted.

Markets reacted positively to Draghi's comments in which he said that further interest rate cuts "remain part of our tools."

The euro was down 0.3 per cent against the dollar, at $1.12.

Trump pounced on this, adding in a later tweet: "European Markets rose on comments (unfair to U.S.) made today by Mario D!"

Aside from rate cuts, other EU stimulus moves could include restarting so-called quantitative easing purchases of government and corporate debt, which amounted to €2.6 trillion between 2015 and 2018.

"The asset purchase program still has considerable headroom," Draghi said.

Since his election in 2016, Trump, a Republican, has been on the warpath against what he describes as the abuse of the United States by its trading partners worldwide.

He pulled out of a major trans-Pacific free trade agreement, forced a rewrite of the NAFTA accord governing free trade among Canada, Mexico and the United States, and is demanding major concessions from allies such as Japan and the European Union.