There are fears that russia may officially view the supply of Western battle tanks and warplanes as entering the war and taking military action in response.

There are informal agreements between NATO countries to refrain from supplying certain weapons to Ukraine.
According to the German news agency DPA, this is due to the risk of a direct military confrontation with russia, which the Alliance wants to minimize, writes ZEIT ONLINE.
There are fears that russia may formally view the supply of Western battle tanks and warplanes as entering the war and taking military action in response. Weapons systems of this type have not yet been delivered to Ukraine.
According to the parliamentary group of the Social Democratic Party of Germany (SPD), this informal agreement is known in Berlin.
“The Defense Committee was fully informed in mid-May”, – Wolfgang Helmich, spokesman for the defense policy of the SPD parliamentary group, told DPA.
According to the NATO representative, all supply decisions, in the end, are the work of individual member countries, writes DPA. So far, they have adhered to informal arrangements, including fears that they will not receive the full support of their alliance partners in the event of a russian attack.
For this reason, Poland, for example, more than two months ago refrained from supplying Soviet MiG-29 fighters to Ukraine, the agency notes.
In March, Todd Commander-in-Chief Todd Daniel Walters said the supply of the MiG-29 was a “high-risk scenario” as it could be misinterpreted by moscow and lead to an escalation between russia and NATO.
And French President Emmanuel Macron said after a special NATO summit on arms supplies: “There is a limit to not being a party to the war”.
Earlier it was reported that President Volodymyr Zelensky stressed that the supply of heavy weapons to Ukraine is the best investment in maintaining stability in the world.
On May 23, the second meeting of the heads of defense departments of several dozen countries took place at Ramstein Air Force Base in Europe.
Following the meeting, US Secretary of Defense Lloyd Austin said that the countries plan to provide Ukraine with Harpoon anti-ship missiles, jet systems, tanks and ammunition.