After US president Donald Trump tweeted that it is not fair to the U.S. taxpayers to spend for NATO expenses, European Council President Donald Tusk fires back.

In a tweet posted before his departure for NATO summit, US president Donald Trump said that it is not fair to the U.S. taxpayers to spend for NATO expenses but European Council President Donald Tusk hits back by saying that Washington has no better ally than the EU.

"The U.S. is spending many times more than any other country in order to protect them. Not fair to the U.S. taxpayer. On top of that we lose $151 Billion on Trade with the European Union. Charge us big Tariffs (& Barriers)!", US president Donald Trump tweeted.

But European Council President Donald Tusk hit back with his own message on the social media site, insisting that the US has no better ally than the EU.

Tusk tweeted: “Dear Donald Trump. US doesn’t have and won’t have a better ally than EU.

“We spend on defense much more than Russia and as much as China. I hope you have no doubt this is an investment in our security, which cannot be said with confidence about Russian & Chinese spending”, European Council President concluded.

Trump sets off for NATO summit in combative mood on military spending, ahead of the summit in Brussels, and he is also due to make his  first visit to Britain, since becoming president.

This week’s two-day summit, beginning on Wednesday at Nato’s new HQ in the Belgian capital, is expected to be dominated by US demands for increased spending by other members of the 29-nation alliance.

Amid increasing tension between Washington and its' allies, US president Donald Trump said to NATO on Thursday that US allies in many cases were worse than our enemies.