Asian markets were mixed while the dollar faced heavy selling Thursday after Moody\'s warned it could downgrade the United States\' top-class debt rating, raising fears of a default by Washington. Moody\'s blamed US lawmakers\' failure to hammer out a deal that would allow President Barack Obama to raise the country\'s debt ceiling, in turn paving the way for it to meet its repayment obligations. With trillions of dollars of US debt held by countries and corporations around the world, a US ratings downgrade would likely send global markets into a downward spiral. Tokyo shed 0.27 percent, or 27.02 points, to end at 9,936.12, with exporters hurt by the yen\'s strength against the greenback, and Sydney closed 0.53 percent, or 24.1 points, off at 4,490.7. Seoul was flat, edging up 0.43 points to close at 2,130.07 while Hong Kong also ended flat, adding 13.32 points to 21,940.20 Shanghai gained 0.54 percent, or 14.97 points at 2,810.44. \"The review of the US government\'s bond rating is prompted by the possibility that the debt limit will not be raised in time to prevent a missed payment of interest or principal on outstanding bonds and notes,\" Moody\'s said. Ratings agency Standard\'s & Poor\'s in April also downgraded its outlook for the US, citing the budget deadlock. The action came as Obama and Democratic lawmakers and their Republican counterparts held a fourth straight day of talks to try to hammer out an agreement on a deficit-reduction budget. Republicans are refusing to lift the country\'s $14.29 trillion debt ceiling without deep government spending cuts, and they reject Democrats\' demand that tax increases must be part of any sweeping deficit reduction plan. The prospect of a downgrade hit the dollar, which has tumbled since the end of last week after poor jobs data and the ongoing eurozone debt crisis, while the yen surges due to its safe-haven status. In choppy Asian trade, the dollar swung above and below its 78.98 yen level from New York late Wednesday. Its volatility was driven by some large-lot purchases from overseas investors, dealers said. At one point both the dollar and euro rose sharply versus the yen before falling back. The euro, which tumbled this week due to fears over the European sovereign debt crisis, was given some respite. The row over US debt took pressure off the euro, which firmed to $1.4198 from $1.4168, and to 112.11 yen from 111.76 yen. The dollar was also lower after Federal Reserve chairman Ben Bernanke told legislators Wednesday that the central bank was \"prepared to respond\" if stimulus was needed to kickstart the ailing US economy. \"The possibility remains that the recent economic weakness may prove more persistent than expected and that deflationary risks might reemerge, implying the need for additional policy support,\" Bernanke said. His comments signalled to some that he was keeping the door open for a third round of quantitative easing. The bank in June wound up its $600-billion \"QE2\" bond purchasing programme that aimed to boost the economy with easy liquidity. Global markets have slumped this week as the eurozone debt woes continue, with fears of a default in Greece spreading to Italy and Spain. Those concerns deepened after Fitch became the last of the three ratings agencies to downgrade Greece to junk status as European officials struggle to hammer out a bailout plan for the beleaguered country. In Sydney, Rupert Murdoch\'s News Corp closed up 3.12 percent despite abandoning its $14 billion bid for the 61 percent it does not own of British satellite television provider BSkyB. He pulled out of the deal amid a phone hacking scandal at the firm\'s British newspapers that has seen the closure of the Sunday tabloid News of the World. Uncertainty in global markets sent gold soaring because of its status as a safe haven. The precious metal closed at $1,582.50-$1,583.50 in Hong Kong -- up from Wednesday\'s close of $1,571.50-$1,572.50 -- after hitting a record high 1,587.97 in London. New York\'s main contract, West Texas Intermediate for delivery in August, was up seven cents to $98.12 a barrel in afternoon trade. Brent North Sea crude for August delivery eased 30 cents to $118.48.