The US Department of Treasury on Wednesday imposed a broad-based package of sanctions against Russian energy, defense and financial services.
The sanctions target the two major banks Gazprombank and Vnesheconombank, and the two major energy firms Novatek and Rosneft, a US senior official told reporters.
"This is a significant step, these financial institutions are among the largest of Russia and routinely access the US capital market to finance their operations. They will no longer be able to do so," said the official.
The sanctions will also designate and block the assets of 8 Russian state owned defense technology firms.
In the weeks leading up to this decision President Barack Obama discussed the plans of creating these sanctions with French President Hollande, German Chancellor Merkel, and English Prime Minister Cameron.
"We have the ability to expand the scope of the actions we took today if Russia continues it provocative behavior," stressed the official.