Investors are pulling out of exchange-traded funds for emerging market bonds at the fastest pace since November after a three-month rally pushed down yields and dimmed the allure of the securities.

U.S.-based ETFs focused on developing-country bonds have posted net outflow of $400 million this month, according to data compiled by Bloomberg through yesterday. That’s bigger than any full month since November, when they lost $406 million.

The extra yield investors demand to hold dollar-denominated debt in developing nations over U.S. Treasuries fell to the lowest since May 2013, when emerging-market assets sank after the Federal Reserve signaled it would trim stimulus. Dollar bonds in developing countries have returned 6.3 percent this year, after losing 5.6 percent in 2013, the most since Bloomberg started compiling the data in 2010.

“After a big rally, it’s becoming tricky now,” Bob Maes, a money manager who helps oversee $4.9 billion in developing- nation assets at KBC Asset Management SA, said by phone from Luxembourg. “The spread is very tight, susceptible to any rise in U.S. Treasury yields. We’ve reduced our outlook for emerging- market external bonds to neutral.”

The yield spread over Treasuries fell to 270 basis points, or 2.7 percentage points, yesterday, the smallest since May 28, according to data compiled by Bloomberg.

Investors pulled $190 million out of the $4.1 billion iShares JPMorgan Emerging Markets Bond ETF, the largest of its kind, on May 1, the biggest one-day outflow since January 2013. A month earlier, the fund attracted a record one-day inflow of $210 million.