WASHINGTON?The number of Americans filing new weekly claims for jobless benefits jumped unexpectedly to 500,000, the highest level in nine months, the government said Thursday, threatening recovery hopes.

The claims in the week to August 14 increased by 12,000 from the previous week's revised figure of 488,000 and came well above most economists' expectations of 475,000.

It was the third straight week in which claims have risen, and underscores the threat posed by unemployment on the recovery from the worst US recession in decades.

It also raised the possibility of authorities taking more stimulus measures to help contain the near double-digit unemployment rate.

"The labor market is weakening, which is making it more difficult to be sanguine about the job market and the recovery's staying power," said Ryan Sweet, economist with Moody's Economy.com.

"Overall, this week's data on initial claims is troubling and it may put pressure on the Federal Reserve to put its contingency plan into motion," he said.

Unemployment is the biggest concern of US President Barack Obama, who is facing an uphill battle to lift the fortunes of his Democratic Party in congressional elections in November.

The Labor Department also said Thursday that the four-week moving average for the new jobless claims, a less volatile indicator than the week-to-week figures, rose to 482,500, an increase of 8,000 from the previous week's revised average of 474,500.

But the total number of Americans receiving unemployment benefits have fallen, the department data showed.

The number of insured unemployed during the week ending August 7 was 4.478 million, a decrease of 13,000 from the preceding week's revised level of 4.491 million.