"Annexing land not part of your country is an act of war. Any Israeli attempt to annex occupied territories will be an offensive act of war." Declaring a country on land that is not yours is an act of war. Any Palestinian attempt to "annex" land by declaring statehood upon it will be an offensive act of war.
Chairman of U.S. Joint Chiefs of Staff says Iran deal lowers near-term atomic arms risk (Reuters)
from the article: Palestinians under world pressure not to declare state unilaterally