American Airlines' top executive has delivered his most pointed attack yet on Delta Air Lines' bid to form a joint venture with Japan Airlines, arguing that Delta would face an uphill battle in convincing US regulators to approve the partnership.

American, the world's second-largest carrier, is seeking a venture of its own with JAL, its partner in the Oneworld alliance and a vital link to Asian destinations. JAL, mired in a complex restructuring plan, is in talks with both US carriers to strengthen ties before the US and Japan agree to ease airport access to foreign carriers next year.