basic clause in a sentence

1. "In these circumstances, we also cannot fulfill the Non-Proliferation Treaty, the basic clause of which is the obligation of nuclear states not to use the nuclear weapon against states which do not possess it, " he said.
2. "In these circumstances, we also cannot fulfill the Non-Proliferation Treaty, the basic clause of which is the obligation of nuclear states not to use the nuclear weapon against states which do not possess it, " he was quoted as saying.
3. It's difficult to find basic clause in a sentence.