Vladimir Putin's critics say he went too far on Ukraine. The former Russian agent who helped trigger the conflict says his biggest mistake was not going far enough.

Putin has made himself a "hostage" to the war in Ukraine by opting not to annex the Donetsk and Luhansk regions after taking Crimea, according to Igor Girkin, the former rebel commander who goes by the name Strelkov, or Shooter.

If the president had sent troops into Donetsk and Luhansk to support the insurgents like he did in Crimea, all of Novorossiya, or New Russia, the term the rebels and their supporters revived to identify a swath of southeastern Ukraine that was once part of the Russian empire, would now be reunited with the motherland, Strelkov said in an interview in Moscow.