BERLIN (Reuters) -Germany will need at least 75,000 additional troops to fulfil its NATO commitments as the alliance adapts its defence planning to face what it sees as an increasingly hostile Russia, Spiegel magazine reported on Friday.

Calls for more troops could present another headache for the German government, which is grappling with how to finance a surge in defence spending since Russia's invasion of Ukraine and has debated re-introducing some form of military service.

At their Vilnius summit last year, NATO leaders signed off on the first major defence plans since the end of the Cold War, detailing how the alliance would respond to a Russian attack.

The move signified a fundamental shift - NATO had seen no need to draw up such plans for decades, as it fought smaller wars in Afghanistan and Iraq, and felt certain post-Soviet Russia no longer posed an existential threat.

NATO and national military planners have been busy translating the plans into concrete requirements, identifying shortages of troops, weapons and other equipment needed to defend against a Russian attack that could, according to the German military's top brass, come as early as 2029.

Based on requirements, allies will have to negotiate which country will fill which capability gaps. Once there is agreement, the requirements will be transformed into NATO's new capability targets for each ally.

The new NATO requirements mean that Germany's armed forces, the Bundeswehr, will need an extra 75,000 troops to fill additional allied corps, divisions and brigades needed to implement the defence plans, Spiegel said, citing confidential documents.

The German defence ministry was not immediately available for comment.

At the moment, the Bundeswehr has some 180,000 soldiers, falling short of the target of around 200,000 troops, and 80,000 civilian employees.

COSTLY PLANS

Defence spending has already become a pinch point for Chancellor Olaf Scholz's three-way coalition in discussions for next year's budget.

Scholz unveiled a 100 billion euro fund in 2022 to overhaul the military. Germany is now set to meet for the first time since the end of the Cold War a NATO commitment to spend at least 2% of gross domestic product (GDP) on defence.

But after overcoming a budget mess at the start of this year, the government is again haggling over how to keep funding the military once the special 100 billion pot expires.

Scholz has backed his finance minister who rejected demands by Defence Minister Boris Pistorius to raise the defence budget, now foreseen at some 52 billion euros ($56.54 billion), by another 6.7 billion euros in 2025.

Pistorius has also tasked his ministry with exploring potential models for re-introducing a form of military service.

(Reporting by Sabine Siebold; writing by Sabine Siebold and Matthias WilliamsEditing by Miranda Murray and Gareth Jones)