Alliances headed by United Airlines and American Airlines are being investigated by European Union regulators over concerns carriers within each group are illegally cooperating on trans-Atlantic routes and prices.

The European Commission, the EU's competition authority, said in a statement yesterday that it will probe cooperation among UAL Corp's United Airlines, Air Canada and Deutsche Lufthansa AG, which are members of the Star Alliance. The other investigation concerns AMR Corp's American Airlines, British Airways Plc and Spain's Iberia Lineas Aereas de Espana SA, which are part of the Oneworld alliance.

"The level of cooperation in question appears far more extensive than the general cooperation between these airlines and other airlines which are part of the Star and oneworld alliances," the Brussels-based commission said in the statement.