BERLIN, June 7 (Reuters) - Germany is looking into buying eight additional F-35 fighter jets made by U.S. defence giant Lockheed Martin, a military source told Reuters on Friday, on top of the 35 jets it has ordered.

Berlin is examining the costs of such a purchase, the source said, with the stealth aircraft seen as the most advanced fighter jet.

In 2022, Germany decided to order 35 F-35s, including missiles and other weapons, for around 10 billion euros ($10.89 billion).

The jets are equipped with advanced sensors and other gear, and Lockheed says it is nearly impossible to track them with radar.

The aircraft will replace the aging Tornado, the only German jet capable of carrying U.S. nuclear bombs stored in Germany.

The German air force has been flying the Tornado since the 1980s, and Berlin has plans to phase it out between 2025 and 2030.

The F-35 will be stationed at an air base near the western German town of Buechel from 2027 and could also carry U.S. nuclear weapons.

The first eight F-35s are scheduled for delivery in 2026 and will be based in the U.S. for pilot training.

Chancellor Olaf Scholz announced what he called a "Zeitenwende", a new era of more assertive foreign policy backed by more military spending, on Feb. 27, 2022, just days after Russia's invasion of Ukraine.

As part of the Zeitenwende, and as a first step to bring the military back up to scratch after decades of attrition following end of the Cold War, Germany set up a 100-billion-euro special fund to purchase modern weapons and pledged to reach NATO's target of spending at least 2% of the national GDP on defence from 2024.

The purchase of the F-35s was the first major defence project the fund was tapped for.

It is unclear, though, how a second batch of jets may be paid for.

The money in the special fund, used to top-up the regular defence budget, has been almost fully allocated and Defence Minister Boris Pistorius has not managed to secure a hike of the 2025 regular defence budget in current budget negotiations.

He argues that the German military will need more money soon or risk procurement being paralysed as there is little funding left for investment.

($1 = 0.9185 euros) (Reporting by Sabine Siebold, editing by Sabine Wollrab, Andrey Sychev, Thomas Seythal and Alex Richardson)