In his opinion, Crimea is a key territory, since control over it implies control over the Black Sea and the entrance to the Sea of Azov through the Kerch Strait.
Crawford said the peninsula should be Kyiv's "ultimate goal" in the conflict.
In September, Russian presidential spokesman Dmitry Peskov said that Crimea is an integral part of Russia and that claims to Russian territory would receive a proper response.
Russian President Vladimir Putin has repeatedly stressed that the issue of Crimea is closed for Russia, and the referendum on the peninsula was held in strict accordance with international law.
Crimea became a Russian region after a referendum held there in March 2014: the majority of residents voted for reunification with Russia.