The United States has suspended negotiations with Russia on restoring a ceasefire in Syria, the State Department said on Monday, blaming Moscow for its military role in the attack on the Syrian city of Aleppo.
The decision followed a threat from U.S. Secretary of State John Kerry last week as Washington is growingly impatient with Moscow on the Syria issue and posed new challenges on the prospects of a political solution to the five-year-old conflict.
"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 reached last month.
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.
As part of the decision on Monday, the U.S. will withdraw personnel that had been dispatched in anticipation of the possible establishment of the Joint Implementation Center with Russia.
However, Kirby said the U.S. 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)."
"Everybody's patience with Russia has run out," White House spokesman Josh Earnest said on Monday, blaming Moscow for undermining the fight against Islamic State and for indiscriminate bombing that has killed civilians and targeted hospitals in Syria.
"There is nothing more for the United States and Russia to talk about," Earnest said.
On Sept. 10, Russia and the U.S. 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.
U.S. President Barack Obama, in a phone conversation with German Chancellor Angela Merkel last week, slammed airstrikes by Russia and the Syrian government on Aleppo.
Obama and Merkel believed Russia and the Syrian government "bear special responsibility for ending the fighting in Syria and granting the UN humanitarian access to besieged and hard to reach areas in Syria," said a White House statement.
In another sign of worsening relations between Washington and Moscow, Russia halted on Monday cooperation with the U.S. on a program for disposal of weapons-grade plutonium.
The Plutonium Management and Disposition Agreement (PMDA) has been halted due to "the emergence of a threat to strategic stability as a result of hostile actions by the U.S. in respect to Russia," as well as "Washington's inability to fulfill its commitments to disposing of surplus weapons-grade plutonium behind its decision," said a document published on the Russian government's website.
First signed in September, 2000 and updated in 2010, the PDMA committed each side to disposal of no less than 34 metric tons of weapon-grade plutonium, enough to produce 17,000 nuclear weapons.
The White House has expressed disappointment over Russia's decision.
"We've obviously been quite disappointed about a range of Russian decisions however both inside of Syria but also in Ukraine," Earnest said. "And unfortunately the announcement about the Plutonium Management and Disposition Agreement is more in line with those kinds of decisions that have only deepened Russia's isolation in the international community."