U.S. Defense Secretary Chuck Hagel says Russia has continued a troop build-up near Ukraine's border despite recent assurances that it has no intention of crossing into Ukraine.
Hagel says the reality on the ground appears to be in contrast to what Russian Defense Minister Sergei Shoigu told him during talks last week.
"The reality is they continue to build up their forces, so they need to make sure that they stay committed to what Minister Shoigu told me."
Hagel commented on Wednesday during a joint news conference with British Defense Secretary Philip Hammond that focused mostly on Ukraine.
Hammond said Shoigu may have little authority when it comes to Russia's actions in Ukraine.
"All the evidence suggests that the Russian agenda is being very much run by President Putin, personally, and other Russian players, including Minister Shoigu, may express views but it's a moot point. We can not know, and we do not know, to what extent all of those people are really inside the inner circle."
Hammond called Russia's annexation of Crimea "unacceptable." He also warned that continued Russian aggression would result in further consequences.
The U.S. has already imposed targeted sanctions against Russia. On Monday, leaders from the U.S. Britain, Canada, France, Germany, Italy and Japan said they were suspending their participation with Russia in the G8 until Moscow "changes course."
On Wednesday, NATO chief Anders Fogh Rasmussen said he joined the U.S. in its call for additional measures against Russia, including updated defense plans, "enhanced exercises and appropriate deployments."
He commented in a statement released after his meeting with U.S. President Barack Obama.