Answer: Nikita Khruschev seals off East Berlin from West Berlin with constractions of a wall dividing Berlin
The note that was sent to Khrushchev was called the "Berlin Ultimatum", which referred to the separation of the world and the Declaration of the GDR as an independent state. In response to this note, American President Eisenhower said that if the USSR plan was implemented, any diplomatic relations would be severed from the country and eventually the situation would lead to the use of military force.