China is the biggest holder of U.S. Treasurys, followed by Japan. Japan's holdings rose to $1.04 trillion from $1.03 trillion in June.

The data is closely watched, since dumping Treasury securities is viewed as one way China could retaliate against the U.S. in an ongoing trade dispute, but bond strategists are skeptical China is really trying to send a message this way.

China's holdings of U.S. Treasury bills, notes and bonds dropped to a six month low of $1.171 trillion in July, from $1.178 trillion in June.

"This is a rounding error. If the Chinese were going to show their displeasure because of the tariffs, this is not where they would do it," said Andrew Brenner of National Alliance. "Would the Chinese rather own Treasurys at 2.80 [percent yield] or 2-year German bunds at minus 0.53? China's not going to show its displeasure in this venue."

Strategists say China is much more likely to retaliate against U.S. tariffs by slapping its own tariffs on American goods, which it has done. Some market pros believe China would use its currency as a weapon before it would dump Treasurys.

"So far China's responses have suggested they really don't want this to go too far. If it becomes all out war, which it's not yet, then there's no reason they wouldn't use everything at thier disposal," said Ward McCarthy, chief financial economist at Jefferies.

The 2-year yield moved up to its high of the day, at 2.80 percent. "The market's traded up a smidgeon," said McCarthy. "But we were at the lows of the day. So far, it's not having much of an effect."