Wal-Mart Stores Inc. said on Thursday that this quarter would be challenging and gave a forecast that suggests profit will again miss Wall Street expectations, due in part to costs from its foreign bribery probe.

The company also reported quarterly earnings just below Wall Street estimates, and revenue came in lower than expected. Everything from tax pressures on shoppers to a cool start to spring led to an unexpected drop in sales at Walmart U.S. stores open at least a year.

Shares of the world's largest retailer fell 2 percent to $78.25 in premarket trading. The stock had hit a new high of $79.96 on Wednesday.

The company forecast earnings of $1.22 to $1.27 per share for its second quarter, which began on May 1. Analysts had been expecting $1.29, according to Thomson Reuters I/B/E/S. The year-earlier profit was $1.18 per share.

In the first quarter, same-store sales at Walmart U.S., by far the company's largest unit, fell 1.4 percent. Both Wal-Mart and analysts had expected such sales to be about flat with those of a year earlier.

Walmart U.S. Chief Executive Officer Bill Simon said a delay in income tax refund checks, a 2 percent increase in payroll taxes and "some of the most unfavorable spring weather we've seen in recent years across much of the country" hurt business in his stores.

Visits to Walmart U.S. stores open at least a year fell 1.8 percent, while the average amount spent per trip rose 0.4 percent.

Sales of warm-weather items, from outdoor furniture and sporting goods to fans and spring clothes, were challenged, particularly from mid-March to mid-April, Simon said. At the same time, price increases in grocery items were lower than expected, "and in fact, we had some deflation in areas like dry grocery," he said on a recorded call.

BRIBERY PROBE COSTS

Wal-Mart is paying tens of millions of dollars to look into possible foreign bribery at international divisions.

In 2011, Wal-Mart began a probe into alleged violations of the U.S. Foreign Corrupt Practices Act and whether the company had handled such matters appropriately.

The issue drew public attention in April 2012, when the New York Times reported that management at Wal-Mart de Mexico orchestrated bribes of $24 million to help it grow quickly in the last decade and that the U.S. parent's top brass tried to cover it up.

Wal-Mart spent $73 million on FCPA work in the first quarter, rather than the $40 million to $45 million it had anticipated. It expects to spend another $60 million to $65 million in the second quarter.

About $44 million of the first-quarter FCPA costs stemmed from ongoing inquiries and investigations, while the other $29 million was for a global compliance review, program enhancements and organizational changes, Wal-Mart said.

MISSING EXPECTATIONS

Wal-Mart earned $3.78 billion, or $1.14 per share, in the first quarter ended on April 30, up from $3.74 billion, or $1.09 per share, a year earlier.

The analysts' average forecast was $1.15 per share, according to Thomson Reuters I/B/E/S. In February, Wal-Mart had forecast a profit of $1.11 to $1.16 per share.

First-quarter revenue rose 1 percent to $114.19 billion. Analysts expected $116.29 billion.

The company said it expected second-quarter same-store sales, excluding those of fuel, to be flat to up 2 percent at Walmart U.S. and up 1 percent to 3 percent at its Sam's Club warehouse store chain.