The IMF's steering committee, made up of 25 of the world's largest economies, said the global outlook was fraught because of weak trade and a series of risks including a UK exit from the EU.
It urged countries to boost public spending and avoid deflation.
The IMF last week made its second cut to global growth forecasts this year.
Christine Lagarde, managing director of the IMF, described the talks between finance ministers and central bankers in Washington DC as "collective therapy" to deal with the gloomy prospects.
But she said calmer financial markets since February had reduced the nerves at the IMF spring meeting.
"There was not exactly the same level of anxiety but I think there was an equal level of concern, and a collective endeavour to identify the solution and the responses to the global economic situation," she said.
The IMF now predicts global growth of 3.2% this year and 3.5% in 2017, having previously forecast 3.4% and 3.6% respectively.
"Downside risks to the global economic outlook have increased since October, raising the possibility of a more generalised slowdown and a sudden pull-back of capital flows," the IMF steering committee said.
It said countries' tax policies and public spending should be "as growth-friendly as possible".
But it also pledged to "refrain from all forms of protectionism and competitive devaluations", amid concerns that some countries are keeping their currencies weak to boost exports.

The dress, studded with 6,000 natural white pearls, was taken from the London Hotel in West Hollywood while Nyong'o was out of the room.
Nyong'o won best supporting actress in 2014 for 12 Years a Slave and was a presenter at Sunday's ceremony.
A statement from the hotel said they were "working with law enforcement".
Lieutenant William Nash, of the Los Angeles County Sheriff's Department, said officers were checking CCTV footage.
Conflicting reports suggested the dress was stolen either on Tuesday night or during the day on Wednesday.
"Ms Nyong'o was not in the room at the time of the theft," Deputy John Mitchell told Reuters.
'Homage'
The dress, designed by Francisco Costa for Calvin Klein, took 25 people 10 weeks to hand-sew the 6,000 Akoya pearls.
On the red carpet on Sunday, the actress told Associated Press she was "just wearing my diamonds and pearls. My homage to (musician) Prince".
Speaking about the dress's design, the 31-year-old said: "We talked about it being fluid and liquid. I wanted it to be an homage to the sea."
No arrests have been made.
Representatives for Calvin Klein declined to comment.
Key countries in the International Monetary Fund (IMF) have pledged to pursue "growth-friendly" policies to kickstart the slowing world economy.
[NEXT_CONCEPT]
A $150,000 (Â£97,000) custom-made Calvin Klein dress, worn by actress Lupita Nyong'o at this year's Oscars, has been stolen in Hollywood.