John Praveen, chief investment strategist at Prudential International Investments Advisers LLC, speculated late last year that China's once-robust purchases of US debt had tailed off because the economic transition had depleted resources.

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"If you're not an export-driven economy and you are more of a consumer-driven economy, your exports will come down, your imports will increase, so your current account deficit will come down," Praveen said. "So they have less money to invest. It may be part of that overall strategy, of reducing how much money they put into the US Treasury market."

Since then, statistics have suggested that the rebalancing has yet to take hold because investment accounted for more than half the nation's economic activity last year. David Dollar, a former US Treasury Department economic and financial emissary to China, said in an interview that although China's gross domestic product grew 7.7 percent in 2013, beating the government's 7.5 percent target, the nation's economy still hasn't seen the increases in domestic consumption and reduction in investment and exports that many economists say would set it on a sustainable course for growth.

Government data showed that capital formation accounted for 54 percent of China's economic growth last year, exceeding the 50 percent share taken up by consumption. Public investment accelerated during the second half of the year as the government sought to boost lower-than-expected growth from the first half of the year.

China's more muted approach to Treasury buying might also reflect a desire to diversify its holdings, Praveen has suggested.

Nevertheless, overall foreign demand for US Treasury securities is expected to remain strong in 2014, helped by the US Congress and the administration reaching an agreement in February that will put off any battle over raising the debt ceiling until March 2015.

The overall outflow in US Treasuries in January surprised observers after benchmark 10-year notes had their best monthly performance since mid-2012, ending the month with 10-year yields at 2.666 percent after starting at 3.038 percent.

Overall, demand for long-term US assets was $7.3 billion, a modest inflow compared with sales of $45.9 billion in December. Analysts said markets were expecting $40 billion in long-term inflow in January.

Excluding swaps and other adjustments, foreigners sold $2.5 billion in long-term US securities in January compared with revised outflows of $51.1 billion the previous month.

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