March 27 (Reuters) - Carnival Corp ( CCL ) cut its annual profit forecast on Friday, as higher fuel costs pressure the cruise operator's margins amid rising geopolitical tensions.

Rising oil prices have lifted fuel costs since the beginning of the conflict in Iran, as attacks on oil and transport facilities across the Middle East and disruptions to energy flows through the Strait of Hormuz have raised concerns about global supply.

The energy price spike threatens Carnival profits as it is the only major U.S. cruise line that does not hedge fuel.

Due to recent fuel price volatility, the company said its guidance is based on fuel purchased in March and early April, with Brent crude assumed to average $90 a barrel for the rest of April and May, $85 in the third quarter and $80 in the fourth quarter, rather than spot prices.

Cruise lines, which rely on heavy fuel oil and marine gas oil among other fuel types, usually turn to hedging to lock in prices via financial contracts and protect against sudden swings.

Shares of Carnival were down 3% in premarket trading.

The company expects full-year adjusted earnings per share to be about $2.21, compared with its previous expectation of up to $2.48.

(Reporting by Koyena Das in Bengaluru; Editing by Shinjini Ganguli)