By Sabine Siebold

VILNIUS (Reuters) -NATO allies on Monday reached agreement on defence plans detailing how the alliance would respond to a Russian attack, overcoming a Turkish hurdle one day before leaders meet for a summit in Vilnius, five diplomats told Reuters.

NATO had for decades seen no need for large-scale defence plans, as it fought smaller wars in Afghanistan and Iraq and felt certain post-Soviet Russia no longer posed an existential threat.

But with Europe's bloodiest war since 1945 raging just beyond its borders in Ukraine, it is now warning that it must have all planning in place well before a conflict with a peer adversary such as Moscow might erupt.

Turkey had been blocking approval of what NATO calls its regional plans over the wording on geographical locations such as Cyprus.

"Excellent for the alliance. Turkey had to compromise and lift linkage," one diplomat told Reuters.

NATO leaders gather in Vilnius on July 11-12 for a summit that will discuss Sweden's membership and the alliance's future relationship with Ukraine.

By outlining its regional plans, NATO will also give nations guidance on how to upgrade their forces and logistics.

The need to finance this fundamental shift is one of the reasons why leaders are set to raise the alliance's military spending target at Vilnius, making the current goal of 2% of national GDP a minimum requirement.

NATO officials estimate it will take a few years for the plans to be fully implemented, though they stress that the alliance can head into battle immediately if required.

(Reporting by Sabine Siebold; additional reporting by Andrew Gray, Andrius Sytas and John Irish; Editing by Rosalba O'Brien)