LOS ANGELES/NEW YORK (Reuters) - FedEx Corp FDX.N reported fourth-quarter profit that beat Wall Street estimates on Tuesday, as revenues and operating margins increased in each of the company's operating units.

FILE PHOTO: A Fedex truck makes deliveries and pick-ups in the Back Bay in Boston, Massachusetts, U.S., June 18, 2018. REUTERS/Brian Snyder

Shares of the Memphis-based package delivery company extended losses in after-hours trading, following their worst regular session sell-off in two months on worries over the U.S.-China trade war.

FedEx is often considered a bellwether for the U.S. economy, along with its main rival United Parcel Service Inc UPS.N. FedEx and companies in the industrial sector faced the brunt of trade tensions on Tuesday after China vowed to retaliate against U.S. President Donald Trump's threat to impose a 10 percent tariff on $200 billion of Chinese goods.

“I have never been so optimistic and so sure of our strategy and our ability to deliver an exciting future,” FedEx Chief Executive Frederick Smith said on a conference call.

He spoke after the company reported a fourth-quarter profit, excluding items, of $5.91 per share - 20 cents per share better than analysts’ average estimate, according to Thomson Reuters I/B/E/S. Revenue matched Wall Street’s target, rising 10.2 percent to $17.3 billion.

Analysts said the latest quarter’s results were buoyed by rate increases, higher package volume, more efficient operations, tax benefits and share buybacks.

“We do remain concerned, however, about threats that manage the free flow of goods among countries. Trade is a two-way street, and FedEx supports lowering trade barriers for our customers, not raising them,” Smith said, echoing comments he made on Friday.

Some analysts and investors are taking a wait-and-see stance.

“At this point we believe it’s more bark than bite,” Edward Jones analyst Logan Purk, said, noting that Trump appeared to be employing a preferred negotiating tactic.

FedEx has been ahead of UPS in making massive network investments to handle the growing number of deliveries for online purchases and other packages, and investors have been eager to see returns.

Those investments paid off in FedEx’s fourth quarter, said Trip Miller, managing director at Memphis-based hedge fund Gullane Capital Partners, who also personally holds FedEx shares.

“We expect that to accelerate over the next three years,” barring a trade war or economic downturn, Miller said.

Shares of both FedEx and UPS closed down about 2 percent on Tuesday. FedEx fell another 0.8 percent to $256.39 in extended trading.

FedEx forecast fiscal 2019 revenue growth of about 9 percent, while analysts were expecting about 6 percent growth.

The company said it expects fiscal 2019 earnings per share of $17.00 to $17.60, excluding some items. The midpoint of that range came in below than analysts’ average estimate of $17.47 a share.