WASHINGTON — An unforeseen burst of hiring last month has lifted hopes that the economy will prove durable once again, even as an array of threats lie ahead.

Businesses across the U.S. economy ramped up their hiring in September, defying surging interest rates, financial market turmoil, the ongoing threat of a government shutdown and an uncertain outlook to add the most jobs in any month since January.

The hiring binge confounded expectations for a slowdown and added one more layer of complexity to the Federal Reserve’s high-wire effort to defeat inflation without causing a recession.

The 336,000 jobs that were added in September raised the average gain for the past three months to a robust 266,000.