UPDATE 2-WTO delays Boeing subsidy report in trade row

* EU says WTO report now due mid-September at the latest

* Airbus says disappointed with report

* WTO says delay due to complexities of the case

* EU warns delay may scupper hopes for negotiated settlement

(Adds more European Commission comment, details)

GENEVA/BRUSSELS, July 8 (Reuters) - The World Trade Organization, citing the complexities involved, delayed on Thursday issuing initial findings in a European Union challenge to the United States over subsidies to Boeing (BA.N).

The decision drew fire from European aircraft builder Airbus (EAD.PA), which called it a disappointment, and from the executive EU Commission.

A trade panel had been expected to issue its confidential interim report on an EU counter-suit over aid to the U.S. aircraft builder on July 16, two weeks after the WTO ruled that Airbus had received prohibited aid from European governments.

"I can confirm that the chairman did speak with the parties and said that due to the complexities of the case there would be a delay in the issuance of the report," WTO spokesman Keith Rockwell said.

Both sides accuse the other of giving illegal aid to their respective plane makers in the world's largest trade dispute.

Although the WTO's findings in the EU counter-case were not expected to be made public for several months, the tit-for-tat subsidy row has been marked by repeated leaks and both sides had been expected to claim victory over the latest draft report.

Airbus and the European Commission criticised the delay.

"The European Commission can now confirm that we were informed yesterday -- on a confidential basis -- that its publication will be delayed until mid-September at the latest," the EU's executive body said in a statement.

"(The delay) creates the wrong impression that Airbus has received some WTO incompatible support, whereas Boeing (BA.N) has not. Only when we have received both panel reports will both sides have a more complete picture of the dispute," the Commission said.

"The European Commission remains confident as to the strength of the EU's legal challenge," it added.

In a separate statement, Airbus Chief Executive Tom Enders said he was surprised and disappointed by the delay.

"Another delay is a disappointment. But we are looking forward to the Boeing subsidies panel report. It will eventually come, and it will show (that) Boeing has received billions of dollars in WTO illegal subsidies," Enders said.

Last Wednesday, WTO judges rebuked the European Union and ordered the EU to eliminate prohibited export subsidies to planemaker Airbus (EAD.PA) which had injured Boeing.

News of the delayed Boeing report comes on the day that Airbus parent EADS filed a bid to supply tankers to the United States in a fierce contest with Boeing.

The EU's executive warned delays could scupper attempts to reach a negotiated settlement and urged the WTO's legal panel to issue its interim report without further delay.

The row over EU and U.S. aircraft subsidies is widely expected to result in a WTO rebuke for both sides, potentially benefiting aircraft builders not involved in the dispute.

(Reporting by Juliane von Reppert-Bismarck, Foo Yun Chee, Tim Hepher, Stephanie Nebehay; Editing by Michael Roddy)