Germany won’t allow allies to ship German-made tanks to Ukraine to help its defense against Russia nor send its own systems unless the U.S. agrees to send American-made battle tanks, senior German officials said on Wednesday.

North Atlantic Treaty Organization allies have over 2,000 German-made Leopard tanks, considered to be among the most sophisticated in the world, according to the London-based International Institute for Strategic Studies.

Several European governments have said they are ready to send German-made tanks to Ukraine, including Poland, Finland and Denmark, if they get approval from Berlin, though none has made a formal request. Britain has said it would send 14 of its Challenger 2 main battle tanks, an older equivalent to the Leopard.

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“One can’t differentiate between direct exports (of German-made tanks) and exports by third countries,” a senior German official said Wednesday.

But the U.S. is “not there yet” when it comes to giving Abrams tanks to Ukraine, Colin Kahl, the Undersecretary of Defense for Policy, the No. 3 at the Pentagon, told reporters on Wednesday.

Read more: WSJ