The Russian military also announced it carried out airstrikes on Islamic State militants in Syria who were preparing an assault on the ancient city of Palmyra, which was liberated from the terrorists earlier this year.
US State Department spokesman, Mark Toner, said the pair agreed to extend the truce over the phone.
"As part of their conversation they [Kerry and Lavrov] discussed and agreed to extend the cessation for another 48 hours, with the goal being that this would last seven days and then we would move to the next step, which is the establishment of the JIC [Joint Implementation Center]", Toner stated.
But the predominant worldwide focus at the moment is sending much-needed aid to besieged areas.
United Nations trucks with a month's worth of food for 40,000 people remain stuck at the Turkish border, two days after a ceasefire came into effect in Syria.
"All these 20 truckloads are ready and they were supposed to deliver them today".
It said government forces will not start pulling out until the rebels begin to do the same.
UN Secretary-General Ban Ki-moon speaks during a press conference at a United Nations school in Gaza City on June 28, 2016.
"It's crucially important [that] the necessary security arrangements" are made so the convoy can travel, Mr Ban said.
I have been urging the Russian government to make sure that they exercise influence on Syrian government and also the American side to make sure that the Syrian armed groups also fully cooperate.
The cease-fire in Syria brokered by the United States and Russian Federation has temporarily put a stop to fighting in some parts of the war-torn country, but it could have unintended consequences that end up working in favor of the leader whom US-backed rebels are trying to oust. "We are very much committed".
The Syrian army has meanwhile accused rebels of numerous violations since the ceasefire took effect.
On Wednesday, both Moscow and Washington spoke positively about the deal, with the Kremlin saying it raised hopes for a peaceful solution to the crisis and Kerry arguing it was a "last chance" to keep Syria together.
One of Syria's most powerful factions, Jabhat Fatah al-Sham's battlefield alliance with other insurgent groups makes it hard for the United States to target them without the danger of inflicting harm on other opposition groups.
One monitoring group reported five violations occurred in and around Aleppo in the ceasefire's first hours, while state-run news agency SANA said rebels were responsible for a number of breaches in Aleppo and Homs.
"From the first minute Russia's been meeting its obligations to enforce the cessation of hostilities in Syria", the defense ministry said in the statement.
The desire for the ceasefire to be successful is being felt by not only Syrian locals, but the greater global community. "The truce is holding".
British Prime Minister Theresa May has told her parliament Syria's future has become intrinsically linked with the rest of world's. The United States and Russian Federation coordinated a partial ceasefire in February, but violence soon resumed.
Once the joint Russian-US targeting begins, however, government warplanes will be barred from areas where either Fateh al-Sham or opposition forces are present. The Syrian government has been heavily criticised for trying to block the aid flows to Aleppo, but it has said they must be coordinated through itself and the UN.
"Thank God the situation is so good".
"They'll be able to see where we believe - and where we will know - that those opposition groups that are allied with the United States are, because we're going to put them on a "do not bomb" list".