Russia's Defense Ministry on Wednesday announced the decision, not long after renewed violence erupted outside of Aleppo in a further reminder of the fragility of previous ceasefire agreements.

"On Russia's initiative, a 'regime of silence' has been introduced in Aleppo for 48 hours from 00:01 16 June (2100 GMT Wednesday) with the goal of lowering the level of armed violence and stabilizing the situation," a ministry statement said. The statement did not say whether Russia discussed the ceasefire with other countries or groups in Syria.

The statement came after US Secretary of State John Kerry called on Russia and Syrian government forces to respect a ceasefire originally agreed upon in February but which has been violated repeatedly by all sides. The State Department confirmed to German news agency DPA that Russia had announced a ceasefire.

"Let me reiterate that the cessation is unlimited by geography or time period," State Department spokeswoman Julia Mason said in an email to DPA. "We are watching closely to see that it can help quell the violence and open humanitarian access to Syrians in desperate need."

Failed peace talks

Discussions meant to bring an end to the five-year war have faltered since representatives of the warring sides agreed to meet in Geneva in May; the talks ground to a halt when representatives of the US-supported rebels walked out.

"The three rounds of talks were unsuccessful because of the stubbornness of the regime and its continued bombardment and aggressions toward the Syrian people," a member of the Jaish al-Islam rebel group said on Twitter last month.

Ongoing tension between Washington, which backs groups like Jaish al-Islam, and Moscow, which supports the government of President Bashar al-Assad, has cast doubt on the likelihood of a peace deal.

German Foreign Minister Frank-Walter Steinmeier on Wednesday called for renewed efforts in establishing a ceasefire.

"The next period will be one of tough negotiations," he said after meeting with Iranian Foreign Minister Mohammad Javad Zarif in Berlin.

Zarif also said there needed to be a "political solution" to the Syrian war.

Criticism of the UN

Also on Wednesday, a Beirut-based advocacy group criticized the UN for favoring the Syrian government when it came to supplying humanitarian aid.

The Syria Campaign, as the group is called, said the UN "allowed the Syrian government to direct aid from Damascus almost exclusively into it territories." As a consequence, the hundreds of thousand of Syrians in need of aid in territories under bombardment by Assad's forces were going without.

In response, the UN said criticism "discredits the work of national and international humanitarian aid workers."

blc/sms (dpa, AFP, AP)