Censor.NET reports citing the letter published on the senator's official website.
"Vladimir Putin's violent campaign to destabilize and dismember the sovereign nation of Ukraine will not stop unless and until he meets a strong and determined response," McCain wrote.
Read more: Ex-KGB chief suspected of helping to compile dossier on Trump
"Therefore, in light of the latest Russian attacks and the prospect of future aggression against Ukraine, I urge you to exercise the authority given to you by the National Defense Authorization Act for Fiscal Year 2017 to provide defensive lethal assistance to Ukraine to defend its territory against further violations by Russia and its separatist proxies.
"At the same time, so long as Russia continues to occupy Crimea and destabilize Ukraine, I implore you to maintain current sanctions against Russia. And based on Russia's attempted interference in our elections, I urge you to expand current sanctions against Russia," the letter reads.
Read more: Senators promise to codify Russia sanctions if Trump fails to reject "reckless course," - McCain
Related materials: President Trump