The head of British Airways’ parent said future members of Europe’s third-largest airline group are welcome to seek deals outside the Oneworld global marketing pact it spearheads.

The comments from Willie Walsh, chief executive of International Consolidated Airlines Group SA, IAG.LN -2.56% highlight the increasingly fluid nature of the global alliances, as well as a split among the largest airlines over the rapid growth of Emirates and its fellow Gulf carriers, Qatar Airways and Abu Dhabi-based Etihad Airways.

American and Qantas both plan to remain in Oneworld, but they are also pursuing deals to pool passengers and frequent-flier programs with Emirates.