The IMF, in its twice annual assessment of global financial stability, said conditions remain broadly conducive to economic growth, but are at risk of worsening should emerging markets deteriorate further or trade tensions escalate.
He contended that China had "already retaliated" against his tariff increases.
The rupiah has indeed been under strong downward pressure, especially over the last three months, as a result of monetary tightening and stronger economic growth in the USA, which has caused higher capital outflows, and the upward trend in global oil prices, which has increased Indonesia's trade deficit and consequently the current account deficit to more than 2.5 percent of gross domestic product (GDP).
Consumer prices in Iran, which rose by 9.6 percent in 2017, are now projected to jump by 29.6 percent this year, and by 34.1 percent next year, the IMF's estimates show. The U.S. economy is expected to grow 2.5 percent in 2019.
Risks to the global outlook have risen in the last three months and tilt to the downside, the International Monetary Fund said. It had previously predicted jobless rates of 5.5% and 5.2% respectively.
The IMF specifically mentioned the situation in Argentina and Turkey - two countries with heavy external debt.
"We are concerned about the downturn in economic growth", noted Jubilee USA Executive Director Eric LeCompte.
"It was decided today that we should start negotiations with the International Monetary Fund for a stabilisation and recovery programme so that we should bring the current hard economic situation under control", Umar said in the message.
Russian Federation was among the few energy-rich emerging market countries whose growth forecasts were bumped up.
"In the case of a flexible exchange regime the national currency, the Pak rupee, would further depreciate to around PKR140 against the USA dollar from the current PKR127".
The IMF expects the U.S. economy to continue growing this year at 2.9%, but sees that rate falling to 2.5% next year amid the country's escalating trade war with China.
"We will be listening very, very attentively when and if they come to us", said Obstfeld.
The model also includes the effects of a reduction in business confidence that reduces investment and leads to a tightening of financial conditions. "In Angola, inflation is projected to fall to 20.5 per cent in 2018 from 29.8 per cent in 2017, and to decline further to 15.8 per cent in 2019", it added.
The effects on the U.S. and China would be particularly severe, with 2019 GDP losses of more than 0.9% in the USA and 1.6% in China in 2019.
In a press conference at the White House on Tuesday, President Trump said "China wants to make a deal and ... they're not ready yet", adding that is a reason his administration has canceled a couple of meetings with Beijing.
It also assumes that Trump imposes a 25% tariff on imported cars and auto parts imports.