WASHINGTON - The United States was suspending negotiations with Russia on restoring a ceasefire in Syria, the State Department said on Monday.

"This is not a decision that was taken lightly," State Department spokesperson John Kirby said in a statement, accusing Russia of failing to live up to its commitments on the ceasefire agreement on Syria.

Russia was "either unwilling or unable to ensure Syrian regime adherence to the arrangements to which Moscow agreed," he added.

The spokesperson also accused Moscow and Damascus of targeting civilian areas and critical infrastructure such as hospitals and preventing humanitarian aid from reaching civilians in need.

In response to Washington's decision, the Russian Foreign Ministry said Monday that the U.S. is trying to shift the blame on Russia.

"Washington has simply failed to live up to the key commitment under the agreements -- to facilitate the humanitarian assistance to residents of the Aleppo city...(and) to apply pressure on the armed opposition groups," the ministry's spokeswoman Maria Zakharova was quoted as saying by the RIA Novosti news agency.

On Sept. 10, Russia and the US announced a landmark agreement on a nationwide ceasefire in Syria, which both sides hoped would lead to their countries' military cooperation to end more than five years of bloodshed there.

However, crossfire resumed in the first hours after the week-long truce deal expired on Sept. 19, with both parties trading accusations of failures to implement the deal.

As part of the decision on Monday, the US will withdraw personnel that had been dispatched in anticipation of the possible establishment of the Joint Implementation Center with Russia.

However, Kirby said the US will continue to utilize the channel of communications established with Russia to de-conflict counterterrorism operations in Syria "to ensure the safety of our respective military personnel and enable the fight against Daesh (the Islamic State)."