Until recently, the United States could argue that it was staying out of the global currency war — letting the dollar appreciate while foreign governments and central banks sent their currencies reeling.

Indeed, the dollar rose to multi-year highs against a wide range of currencies in recent months.

"But things look different today, and U.S. officials’ exchange-rate jitters are becoming increasingly pronounced," star economist Nouriel Roubini of New York University writes on Project Syndicate.

"The dollar appreciated much faster than anyone expected. And the impact on net exports, inflation, and growth has been larger and more rapid than that implied by policymakers’ statistical models."

So what are the ramifications?

"The U.S. has effectively joined the currency war to prevent further dollar appreciation," Roubini maintains. "Federal Reserve officials have started to speak explicitly about the dollar as a factor that affects net exports, inflation and growth.‎"

Already, the euro has risen 7 percent from the 12-year low it hit March 13, trading at $1.1151 Monday afternoon.

And the U.S. attack isn't over, Roubini says. "Verbal intervention will be followed by policy action, because slower growth and low inflation — partly triggered by a strong dollar — will induce the Fed to exit zero policy rates later and more slowly than expected."

The central bank has kept its federal funds rate target at zero to 0.25 percent since December 2008, and most economists don't expect an increase until at least September.

Meanwhile, Microsoft co-founder Bill Gates warns that near-zero interest rates around the globe spawn grave potential danger.

"The environment with low interest rates — it's globally so unusual. It really shouldn't persist," he told CNBC. "It creates problems in terms of leverage and bubbles."

Some experts think the Fed already has created bubbles in some financial markets, including stocks. The S&P 500 index has tripled over the past six years.

But exiting low rates isn't so easy, Gates notes. "How do we get out of it without creating some economic setback? It would be very difficult," he said.

While the Fed debates when to begin raising rates, many central banks overseas are keeping theirs low. "People do expect the U.S. to sort of take the lead in pushing our way out of this situation," Gates said.

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