Passage: The Antarctic Treaty and related agreements regulate international relations with respect to Antarctica, Earth's only continent without a native human population. The treaty has now been signed by 48 countries, including the United Kingdom, the United States, and the now-defunct Soviet Union. The treaty set aside Antarctica as a scientific preserve, established freedom of scientific investigation and banned military activity on that continent. This was the first arms control agreement established during the Cold War. The Soviet Union and the United States both filed reservations against the restriction on new claims, and the United States and Russia assert their right to make claims in the future if they so choose. Brazil maintains the Comandante Ferraz (the Brazilian Antarctic Base) and has proposed a theory to delimiting territories using meridians, which would give it and other countries a claim. In general, territorial claims below the 60° S parallel have only been recognised among those countries making claims in the area. However, although claims are often indicated on maps of Antarctica, this does not signify de jure recognition.

Question: What two countries prohibited new claims on Antarctica?
The Soviet Union and the United States