After sounding the alarm in recent years about threats to the global economy, International Monetary Fund chief Christine Lagarde said Monday the risks had begun to materialize and were now slowing growth.

In a speech just hours after the United States, Mexico and Canada announced a revised North American trade agreement, Lagarde said the rise in trade barriers "is hurting not only trade itself, but also investment and manufacturing as uncertainty continues to rise."

She signaled that the IMF would downgrade its global growth forecast next week, and urged governments to de-escalate disputes.