Here's why Treasury yields will keep on falling

How low will yields go?
How low will yields go?

Don't bet against the U.S. bond market rally anytime soon.

Conflicts in Ukraine and the Middle East, and record low bond yields in Europe, have unleashed a stampede into Treasurys, knocking benchmark 10-year yields to 2.30 percent, a 14-month low at one stage on Friday. They ended the week at 2.34 percent.

The U.S. bond rally, which accelerated on Friday after Ukraine claimed its artillery destroyed part of a Russian armored column that entered its territory, has shown earlier market calls from some leading bond investors, such as DoubleLine's Jeffrey Gundlach, to be on the money.

Read MoreGundlach: Could see 10-year go to 2.2%

"We are in a market environment now that is largely beyond fundamentals," said Chris Orndorff, portfolio manager at Western Asset Management in Pasadena, California, a leading U.S. bond manager that has about $470 billion in assets. "The falling yield levels are a reaction to panic, as U.S. Treasurys continue to play the role that they have always played, the favorite asset in a flight-to-quality environment."

U.S.-based funds that invest primarily in Treasurys have attracted inflows for four straight weeks, accumulating more than $4.5 billion of new investor cash in that run, according to Lipper, a unit of Thomson Reuters. The four-week moving average of flows shows investors moving into this sector at the fastest pace in nearly six months.

Meanwhile, more speculative investors such as hedge funds, have reversed their recent short positions in 10-year Treasury futures and options. The latest week's Commitments of Traders data from the Commodity Futures Trading Commission showed speculators were net long by about $374 million after being net short by $616 million the week before.

Read MoreBond yields plunge on fresh Russia-Ukraine tensions

The latest bull run in bonds has defied expectations of those traders and investors who had bet on U.S. interest rates rising this year as the U.S. jobs picture improved and the Federal Reserve paved the way to tighten policy in 2015.

Bond yields could decline further if, as expected, Fed Chair Janet Yellen reiterates her concerns about underlying weakness in the labor market in her speech next week at a global central bankers conference in Jackson Hole, Wyoming.

"She is going to remind us why they would maintain a dovish policy stand," Jeffrey Rosenberg, chief investment strategist for fixed income at New York-based BlackRock, the world's biggest asset manager with $4.3 trillion in assets.

Read MoreFed has a lesson plan, but traders just want facts

Bond analysts and managers interviewed by Reuters on Friday said the 10-year yield could fall another 10-15 basis points. They didn't rule out it reaching the 2 percent level in the current rally.

Still, they warned that if global political tensions ease, the safe-haven demand for U.S. bonds will subside. Then, the 10-year yield could snap back to 2.60-2.70 percent.

Rock-bottom European yields

Why it's time to play defensive in US markets
Why it's time to play defensive in US markets

Foreign demand for U.S. Treasurys has also grown in recent weeks because the yields on German and other European government bonds continue to fall.

The benchmark 10-year U.S. Treasurys yield has been running more than 1.30 percentage points above the yield on 10-year German Bunds since the beginning of July. This premium is the biggest since June 1999, which was before the euro was introduced.

Some big bond investors like Pimco's Bill Gross, who manages the world's biggest bond fund with $223 billion in assets, see Treasurys gains tied closely to the movement in Bunds. That's because the consistently wide spread between the two makes it an attractive carry trade for European-based investors to sell Bunds and buy Treasurys. With the euro declining, investors would also get a positive currency benefit.

This week, data showing anemic second-quarter growth across the euro zone, suggesting the 18-nation block is close to deflationary conditions. The European Central Bank is expected to fight aggressively to prevent deflation from taking root by providing more easy money, which in turn could see European bond yields fall further.

Read MoreEuro zone growth stagnates, Germany contracts

"European government bond pricing is reaching an inflection point, which will force the ECB to act," said Larry Jeddeloh, chief financial officer of the TIS Group, which produces the Market Intelligence Report.

This week, the German 2-year yield fell into negative territory while its 10-year yield dropped below 1 percent for the first time ever. Italian and Spanish yields fell to record lows in step with their German counterparts.

"This pulls global allocation into the United States," said BlackRock's Rosenberg.

He said that Asian investors dealing with a stuttering Japanese economy and fears of slower growth in China have been shifting more money into U.S. debt.

The yield on 10-year Japanese government bonds ended Friday at 0.51 percent, 1.83 percentage points below the 10-year U.S. yield.