EU transport ministers want more details on US proposals to relax rules on foreign ownership of airlines before any Open Skies deal is signed.
The ministers agreed at their meeting in Brussels on Monday that good progress had been made in talks last month in Washington.
But they want the US to clarify its plans to ease its current strict regulations on foreign ownership of airlines operating in America.
A public consultation on the relaxation of foreign ownership rules is also being carried out in the US and the European ministers also want to hear the result of that before agreeing any deal to liberalise the transatlantic skies.
After the meeting on Monday, Britain, current president of the EU, said there would be no deals until European concerns on the US ownership rules were taken into account.
Present US rules prevent foreign interests owning more than 25% of a US carrier or 49% if the foreign stakeholder's country has an open skies deal with America.
"Until everything is agreed, there is no agreement. Make no mistake about that," Alistair Darling, the UK transport secretary, said.
He said the latest deal which proposed to allow any US airline to fly from the USA to any European airport and any European carrier to fly from Europe to any US airport was substantial progress.
But he added: "What we were saying today is yes, so far so good, however there is still a big amount to be resolved."
Mr Darling also said that the transport ministers refused to give EU officials authority to negotiate an Open Skies deal with China.
They said it would be "premature" to start talks with China while they were still engaged in detailed discussions with the Americans.