IMF chief economist Maurice Obstfeld said U.K. growth predictions were lowered due to the British economy's "tepid performance" | Manan Vatsyayana/AFP via Getty Images IMF downgrades UK, US growth forecasts Fund downgrades British economy for first time since Brexit vote.

The International Monetary Fund lowered its growth forecasts for the United Kingdom and the United States Monday and revised up its expectations for several eurozone countries including France, Germany, Italy and Spain.

The IMF said its global growth projections from this year's April World Economic Outlook remain on track, with 3.5 percent global growth expected this year and 3.6 percent in 2018. But in its July World Economic Outlook report, the fund said it expects the British economy to grow by 1.7 percent this year, a decrease of 0.3 percentage points from its April assessment. It is the IMF's first downgrade of Britain's economy since the country voted to leave the EU in June 2016.

The IMF kept global growth predictions unchanged due to stronger than expected growth in the eurozone, Canada and Japan, according to its report. Growth in China also remained steady, with only modest declines predicted in 2018.

The fund also revised down its U.S. growth forecasts due to uncertainty over fiscal policy, to 2.1 percent from 2.3 percent this year and to 2.1 percent from 2.5 percent in 2018.

Speaking at the launch of the report in Kuala Lumpur Monday, IMF chief economist Maurice Obstfeld said U.K. growth predictions were lowered due to the British economy's "tepid performance," the Guardian reported. “The ultimate impact of Brexit on the United Kingdom remains unclear," Obstfeld added.

Later, Obstfeld told BBC Radio 4 the IMF had long predicted Brexit would have negative long-term effects on Britain, and said things could get worse, depending on the outcome of the country's Brexit negotiations with the EU. Obstfeld said current predictions were based on relatively "optimistic projections" of the outcome of the talks, but if negotiators are not reasonable and willing to compromise, further downgrades were possible.

Obstfeld said current IMF predictions incorporate some sort of equivalency for British financial services firms in the EU, but if negotiators fail to reach a deal for sector, the country's economy would likely suffer further.

This article was updated with further comments from Maurice Obstfeld.