Rating agency Moody's warned Wednesday that a slowdown in global growth linked to China and a rise in U.S. interest rates are two key reasons why it could lower its credit grades for countries next year.

Though the agency's overall view is that a "shallow" economic recovery around the world should help shore up the ratings it assigns to countries, it said there's potential for some downgrades in 2016 and that risks are "tilted to the downside."

In a wide-ranging report, the agency cautioned that a rate hike by the U.S. Federal Reserve, which would be its first in more than nine years, could hit emerging market countries. Investors have used low interest rates in the U.S. to borrow money to invest in higher-growth, riskier economies around the world.

Moody's said higher U.S. interest rates will create more uncertainty for countries like Turkey, Tunisia, Venezuela and Argentina, that have in recent years benefited from foreign investment. It does not, however, forecast a crisis in emerging markets.

The agency also warned that a sharp slowdown in China would have "broad implications and negatively affect trading partners and economies that are highly dependent on commodity exports."

China has been the main locomotive of the world economy over the past few years but its growth is now coming off the boil. Though its economy is still expected to grow about 6-7 percent range in the coming year, that is much slow than in the previous few years.

Jitters over China's economy have become more acute this year, notably in August, when global stock markets suffered one of their biggest routs since the dark days of 2008-9.

Since China has been a voracious consumer of energy and raw materials, its slowdown has helped push down oil and commodity prices, hurting the countries that produce such goods.

"Lower growth, and the related fall in commodities prices, damages sovereign fundamentals," Moody's said.

Though the agency said most countries are "resilient" to lower growth, it noted "vulnerabilities." Moody's said less diversified and generally smaller, open economies such as Mongolia, Bahrain, Oman and Ghana are most vulnerable.