BEIJING (Reuters) - China has been dethroned by Japan as the top holder of U.S. government debt as the Chinese central bank has dipped into its foreign exchange reserves to support the yuan, while its Japanese counterpart has been content to allow the yen to weaken.

A U.S. one-hundred dollar bill (C) and Japanese 10,000 yen notes are spread in Tokyo, in this February 28, 2013 picture illustration. REUTERS/Shohei Miyano

Investors are paying close attention to declines in China’s holding of U.S. Treasuries as any sharp sell-off could add further upward pressure to U.S. interest rates, which in turn can undermine the Chinese currency.

Figures for foreign ownership of U.S. Treasuries in October released late Thursday in Washington confirmed the shift, with China’s stock of U.S. federal debt plunging to the lowest in more than six years.

On Wednesday, the U.S. Federal Reserve raised interest rates and signaled a faster pace of rate increases in 2017, sending yields on shorter-dated Treasuries to their highest levels in more than five years.

U.S. President-elect Donald Trump’s attacks on Beijing over its trade and currency policies, as well as his questioning of the stance of current and past U.S. administrations concerning Taiwan, has triggered fears that China could decide to sell U.S. Treasuries in response.

However, Chinese government policy advisers, who declined to be identified because of the sensitivity of the subject, say they believe that’s highly unlikely.

An official at the news department of the People’s Bank of China, the nation’s central bank, declined to comment.

In October, China’s holdings of U.S. Treasuries fell by $41.3 billion to $1.115 trillion, according to data from the U.S. Treasury Department. It marked the fifth straight monthly drop and brought the total China has sold off over the previous 12 months to $139.2 billion, the third-largest annual decline ever.

The more important figures will be for November and December, which will not be released until some weeks into next year. They will show what happened after Trump won the U.S. presidential election on Nov. 8,, and investors sold off Treasuries in anticipation of rising U.S. economic growth and larger U.S. government budget deficits, as Trump plans to cut taxes and borrow to fund new infrastructure spending.

China’s reduction of its holdings of Treasuries in the autumn may well have helped it avoid some hefty losses.

Treasuries prices have slumped since the election, and investors have faced a negative total return of 3.3 percent in that time, according to the Bank of America/Merrill Lynch U.S. Treasury Index. Losses have been particularly steep in longer-dated paper, with the 10-year note falling 5.7 percent and 30-year bond losing 10.3 percent, both on a total return basis.

Japan’s move into the top spot came as it also cut its U.S. Treasuries stake, although by a far-smaller amount, about $4.5 billion, to $1.132 trillion in October. Its holdings have fallen by about $17.3 billion from the previous October.

Japan’s holdings eclipsed China’s for just one month in February 2015, the first time since the 2008-2009 global financial crisis.

“China has been selling dollars to keep the yuan steady while Japan is very happy to let the yen depreciate,” said Chester Liaw, an economist at Forecast Pte Ltd, Singapore.

TIGHTROPE WALK

Economists say they expect China to continue to reduce its holdings of U.S. government debt, considered as the most liquid dollar assets, to help defend the yuan, but a big sell-off looks unlikely.

The yuan <CNY=CF XS> fell to its weakest level against the U.S. dollar in more than eight years on Thursday, after the Federal Reserve’s rate rise and outlook.

“China has been consciously cutting its holdings of U.S. Treasuries, to defend the yuan, and it’s hard to stop this trend,” said Zhou Hao, Singapore-based economist with Commerzbank.

China’s foreign exchange reserves, still the world’s largest, have fallen by $942 billion from a peak hit in June 2014, to a six-year low of $3.052 trillion in November, a drop of 24 percent. Meanwhile, China has reduced its U.S. Treasury holdings by $111 billion between June 2014 and September this year, a drop of 9.0 percent.

The PBOC is likely to spend more of its reserves to support the yuan, although it’s walking on a tightrope, seeking to slow the yuan’s descent while trying to preserve the reserves by reducing capital outflows through tighter controls.

Some traders believe the $3 trillion mark is a key psychological level for the PBOC, but it risks rapidly churning through its remaining stockpile of reserves if the U.S. dollar keeps climbing and Beijing has to fight to steady the yuan.

Some Chinese government economists have put the minimum prudent level of reserves at somewhere between $1.62 trillion to $2 trillion.

MUCH DEPENDS ON TRUMP

One central bank adviser said earlier this month that China should use its foreign reserves to help maintain market confidence in the yuan, as expectations of further depreciation have led the exchange rate to weaken too far against the U.S dollar.

But government policy advisers do not believe that dumping U.S. Treasuries is among policy options to be considered by top leaders, even if China wants to retaliate against the United States. That will, of course, also depend on whether Trump carries through on his threats to declare China a currency manipulator, impose punitive tariffs on Chinese imports into the U.S., and whether he abandons the ‘One China’ policy.

Liquidating a big chunk of U.S. debt holdings could roil financial markets and force the United States to scramble for funds, but analysts believe such a move by Beijing would risk starting a fire sale in which the value of its own portfolio would burn.

There are few alternatives to U.S. government bonds, with their negligible risk of default and positive yields.

“This (dumping U.S. debt) is a bad idea. It will not be among retaliatory measures to be considered by the government,” said one Chinese government policy adviser.