Global economic growth in 2019 should be even slower than previously expected but a little bit of upswing is expected, the head of the International Monetary Fund (IMF) said Tuesday.

"The largest uncertainty that we have is trade tension which has really fueled this anxiety of economic operators around the world," said IMF chief Christine Lagarde.

Lagarde said she's optimistic about a trade deal being finalized as both parties have a lot at stake and have a lot to preserve by concluding and reaching a final deal that would be comprehensive between them.

She added that the IMF has calculated the impact of a 25-percent increase in the tariffs on all trade between the U.S. and China. It's a reduction of the U.S. GDP of 0.6 percent, and China's GDP of 1.5 percent. The impact is quite heavy and would inflict a blow on the global economy as a result.

"The impact of the resolution of tensions will depend on how constructive, comprehensive and definite it is," said Lagarde. The deal will certainly encourage economic cooperation and that will give a framework within which they can invest, develop and create jobs, if it is comprehensive and addresses issues such as intellectual property protection, transferred technologies, the definition of state-owned enterprises, and the role they play, she added.

Lagarde said that the forecast for growth is different from what it was a few years ago. China's development can clearly afford and should afford to focus on quality growth, rather than simply quantity growth. The country should focus on quality growth and focus on control of the credit system as it is turning the model around from being predominantly export and investment driven, to be more domestic and consumer driven.

The IMF advocates for a strengthening of the euro area by completing a solid banking union and deepening a euro area security market in order to resist the next crisis. But both are unfinished at the moment. Speaking of next week's spring meetings in Washington with the World Bank, Lagarde hopes the finance ministers will focus on structural reforms, monetary policy and fiscal policy at home in order to secure growth momentum.