China is calling on the United States to protect the interests of its investors as its politicians engage in a policy battle that has brought it to the brink of default.

At a foreign ministry briefing Thursday, spokesman Hong Lei said China hopes the U.S. government will adopt “responsible policies and measures to guarantee the interests of investors.”

China is the largest U.S. creditor with more than $1 trillion invested in the United States, which has long been considered a safe harbor with the highest possible credit rating.

However Moody’s Investment Service warned Wednesday it was putting the U.S. rating on a downgrade watch because of uncertainty over the negotiations to raise the American debt ceiling. The Chinese credit rating agency Dagong took a similar action on Thursday.

China has been gradually reducing its holdings in U.S. Treasury bonds since late last year. However the figure increased slightly in April to $1.153 trillion, according to U.S. data.

Dagong said Thursday it believes slow economic growth and large budget deficits will make it more difficult for the United States to meet its debt obligations over the next couple of years.