The Turkish parliament has passed a motion granting US aircraft the use of Turkish airspace for the war against Iraq.
The US is still in talks with Turkey on possible troop deployment
The bill will allow military overflights from Europe and airlifts of US-led troops into Kurdish-controlled areas of northern Iraq, enabling them to open a second front.
It also authorises the entry of Turkish troops into the same area to stem a potential tide of refugees and prevent the Kurds forming a separate state.
The new motion, which was passed by 332 votes to 202, leaves most of the US's military requests unfulfilled.
Turkish Prime Minister Recep Tayyip Erdogan has said the US will not be permitted to use Turkish airbases, even for refuelling.
Let the decision be beneficial to our people
Neither will US ground troops be allowed to cross into Iraq from Turkey.
But the BBC's Nick Thorpe in Ankara says permission to use Turkish airspace will make military flights from Europe to Iraq much easier.
He says the decision to allow Turkish troops into northern Iraq will alarm both the Kurds and the US, which fears possible clashes between Kurds and Turkish forces.
Ankara has said the US agrees in principle to a Turkish troop presence in the region - but US officials say they oppose a unilateral incursion.
Mr Erdogan seemed happy with the outcome.
"Let the decision be beneficial to our people," he said.
"This was a result I expected."
There is strong public opposition to a war
However, US officials have said that there will be no financial compensation for granting airspace rights.
A multi-billion-dollar aid package was painstakingly negotiated between Ankara and Washington earlier this month, when the US was seeking permission for 62,000 soldiers to be allowed into Turkey, to open a northern front.
Justice Minister Cemil Cicek said on Wednesday that a motion on US troop deployments could be put to parliament at a later date.
Turkish officials have made clear that US and UK aircraft patrolling the UN's no-fly zone from bases in Turkey are not to become involved in the US-led attacks.
There is strong Turkish opposition to a war in Iraq, but correspondents say the country's leaders are worried about alienating the US.