The US job market continues to strengthen with the number of Americans applying for unemployment benefits now at a four-year low, the labor department said Thursday.

For the week ending March 17, initial jobless claims fell by 5,000 to a seasonally adjusted 348,000. The four-week average of applications, a less volatile measure, dipped to 355,000.

A drop in jobless claims has coincided with the highest rate of hiring in two years. Employers added an average of 245,000 jobs per month from December to February. Joblessness has now fallen to 8.3%, its lowest level in three years.

The latest figure will be another boost for President Barack Obama who has put the economic recovery at the center of his re-election campaign.

With the jobs market clearly improving, his Republican rivals have shifted their attack to rising gas prices. "With the economy looking like it's getting a little better on the employment front, gasoline's getting a lot worse," Mitt Romney told a crowd at a town hall meeting in Illinois this week.

But some, including former Obama aides, have warned that the recovery in the job market may fizzle.

"I think the main thing that [President Obama] ought to worry about is that the growth rate is probably not as sustainable at as high a rate as it's been, so the pace of expansion, which for six months has been pretty impressive, it may just slow down a bit," Austan Goolsbee, Obama's former economic adviser, told ABC's This Week.

According to Thursday's report the number of people continuing unemployment benefit claims fell by 9,000 to a seasonally adjusted 3.35 million in the week ended March 10.

Gud Faucher, senior economist at PNC Financial Services, said he would expect the US to add another 200,000 plus jobs in March. The latest in the closely-watched non-farm payroll figures are released in the first week of April.

"There are concerns out there about oil prices and about Europe, although those are lessening. But on the other hand the recovery is gaining some momentum," he said. "After what we have been through, consistent jobs growth of around 200,000 a month is going to start to make people feel an awful lot better."