The United States and Russia agreed that the Syrian cessation of hostilities that began on Monday had largely held and should be extended for another 48 hours despite sporadic violence, the U.S. State Department said on Wednesday.

The cessation of hostilities, brokered by U.S. Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov on Friday, went into effect on Monday night.

State Department spokesman Mark Toner said Kerry and Lavrov had spoken by telephone earlier on Wednesday and agreed it was worth extending the truce.

Under the deal, the United States and Russia are aiming for reduced violence over seven consecutive days before they move to the next stage of coordinating military strikes against Nusra Front and Islamic State militants, which are not party to the truce.

"There was agreement that as a whole, despite sporadic reports of violence, the arrangement is holding, and violence is significantly lower in comparison with previous days and weeks," Toner told a briefing.

"As part of the conversation they agreed to extend the cessation for another 48 hours," he said.

The Syrian Observatory for Human Rights, which monitors the Syrian conflict through contacts on the ground, said no deaths from fighting had been reported in the first 48 hours of the truce.

"This recommitment will initially be for 48 hours, and, provided it holds, the U.S. and Russia will discuss extensions, with the aim of achieving an indefinite extension to lower the violence," Toner explained later.

He said Russia needed to use its influence over Syrian President Bashar al-Assad to ensure that humanitarian aid was delivered to besieged communities under the agreement.

"We haven't seen the humanitarian access yet so we're still continuing to assess this, talking to the Russians," he said. "We're pressuring them to pressure the Assad regime."

Two aid convoys, each of around 20 trucks carrying mostly food and flour, that were headed for the city of Aleppo have been held up since crossing the Turkish border, according to United Nations and other officials.

The U.N. special envoy for Syria, Staffan de Mistura, said on Tuesday the United Nations was waiting for Damascus to issue letters authorizing the aid deliveries, which are desperately needed in Aleppo, the scene of Syria's fiercest fighting in recent months.

The U.N. has estimated that well over half a million people are living under siege in Syria.

The five-year-long civil war in Syria has left hundreds of thousands of people dead and more than 11 million people have been displaced.

(Reporting by Lesley Wroughton; Editing by Paul Simao, Toni Reinhold)