US airline shares tumbled on Tuesday after ratings downgrades on several carriers said they remain vulnerable to industry pressures.

American Airlines parent AMR and US Airways Group were down nearly 6 percent after their downgrades, while Continental Airlines, which Merrill Lynch also downgraded, shed nearly 5 percent.

Analyst Michael Lindenberg said in a research note that airlines are likely to enjoy a strong June quarter, but cited rising fuel prices and other industry issues.

Calyon Securities analyst Ray Neidl linked the drop in airline shares on Tuesday to the Merrill outlook. "I've got a feeling it might only be temporary," he said.

Airline shares were down broadly in early trade. The Amex airline index was down 3.5 percent.

AMR was down 5.5 percent at USD$26.13 on the New York Stock Exchange, where Continental was down 4.7 percent at USD$30.23 and US Airways fell 5.8 percent to USD$52.56.