U.S. investors looking to make a bet on companies in Kazakhstan or Qatar are getting help from an exchange-traded funds industry that is increasingly adding single-country ETFs to their offerings.

Some 30 new single-country ETFs came to market last year focusing on markets ranging from the United Arab Emirates to South Korea and China. That brings the total to 202 single-country ETFs with $97.2 billion assets in the United States, more than double the number of funds that existed five years ago.

Dozens more––including one aimed at Kazakhstan––are in registration with the U.S. Securities and Exchange Commission.

Darshan Bhatt, chief investment officer of Jersey City, New Jersey-based Glovista Investments LLC, which manages about $1.1 billion, picked Vietnam as a good place to invest, based on its growth potential. Last year, Bhatt bought shares in the Market Vectors Vietnam ETF.

"It's important for us to have these single country funds," said Bhatt, whose firm runs a strategy that seeks to outperform the MSCI Emerging Markets benchmark index, which can involve turning to "off benchmark" nations like Vietnam that they favor. 

The fund includes Vietnamese companies including food processing firm Masan Group Corp, property conglomerate Vingroup and Sacombank.

Still, focusing on a single market overseas can carry risks and requires monitoring. Government restrictions can limit the supply of securities available to U.S. fund managers, and the funds' pricing can be unpredictable because they can trade all day on U.S. exchanges while the markets they track are closed.

As a result, the ETF prices don't always match the value of their underlying assets, as they do in traditional mutual funds that price once a day. Single-country ETFs often sell at either a discount or a premium, and they can hit unwary investors.

The average maximum premium for all single-country ETFs was 3.2 percent, while the average maximum discount was minus 2.9 percent over a 12-month period, according to a Reuters analysis of data provided by ETF.com.

By comparison, the maximum premium at the SPDR S&P 500 ETF, a major U.S. domestic ETF, was 0.14 percent and its maximum discount was minus 0.08 percent.