By Sabine Siebold, Humeyra Pamuk and Tuvan Gumrukcu

ANTALYA, Turkey (Reuters) - Germany on Thursday backed U.S. President Donald Trump's demand to more than double NATO's defence spending target to 5% of GDP, as Washington urged countries to eliminate any "weak links" in the alliance caused by a lack of military investment.

"We are following him (Trump), and we see this as a clear commitment by the United States to NATO's Article 5," Germany's new Foreign Minister Johann Wadephul said, referring to the military alliance's mutual defence pact.

Wadephul, who took office earlier last week as part of a new conservative-led government, was speaking at a meeting of NATO foreign ministers in the Turkish city of Antalya, where defence spending was high on the agenda.

NATO's current defence spending target is 2% of GDP - a goal currently met or exceeded by 22 of its 32 members. But many NATO leaders say that target is now too low, as they see Russia as a much greater threat following its 2022 invasion of Ukraine.

With six weeks to go before NATO leaders hold a summit at The Hague, member countries are striving to satisfy Trump's demands, aiming to prevent a recurrence of past threats by the U.S. president to withdraw from the alliance or weaken the U.S. commitment to collective defence.

NATO chief Mark Rutte has proposed a two-pronged approach to meet Trump's 5% call, suggesting allies spend 3.5% of their GDP on defence and dedicate a further 1.5% to broader security-related issues such as infrastructure and cyber security.

Thursday's meeting was the first opportunity for foreign ministers to discuss the proposal.

Some countries had previously made clear they saw 5% of GDP as an unrealistic target, at least in the near term. At the other end of the spectrum, some are unhappy with the idea that not all of the 5% would go on core military spending.

"The target for NATO member states should be 5% in the future. And we are not talking about anything else but real defence spending, what is defined in NATO rules," Estonian Foreign Minister Margus Tsahkna said in Antalya.

U.S. Secretary of State Marco Rubio used a more emollient tone on NATO than some members of the Trump administration, who have sparked European fears about Washington's commitment to an alliance that relies heavily on U.S. military power.

But he made clear the U.S. expected its allies to step up their defence spending.

"NATO has the opportunity to grow even stronger. The alliance...is only as strong as his weakest link and we intend and endeavor to have no weak links in this alliance," Rubio told reporters in Antalya before the meeting.

Rutte said he was optimistic that more countries will reach the current NATO target before the summit.

"It now seems that we will get very far in bringing the whole of the alliance to the 2%, that will build the launching platform for the summit," he said.

(Reporting by Sabine Siebold, Humeyra Pamuk and Tuvan Gumrukcu in Antalya; Editing by GV De Clercq and Toby Chopra)