A woman carries an injured boy inside a hospital after multiple suicide bombings claimed by the Islamic State group struck near Syria's capital and the city of Homs. SANA via REUTERS

The Islamic State group has said it was behind a string of suicide bombings near a Shiite shrine outside Syria's capital and in Homs that killed more than 150 people on Sunday, as Washington and Moscow worked to secure a cease-fire.

The bombings occurred as US Secretary of State John Kerry said a provisional deal had been reached on the terms of a truce in Syria's brutal conflict.

Near Damascus, a car bombing followed by two suicide attacks ripped through the area of the Shiite shrine of Sayyida Zeinab and killed 96 people, according to the Syrian Observatory for Human Rights.

Syria's official news agency, SANA, quoted a police source as saying that 178 people, including children, were among the wounded.

An AFP reporter said the blasts struck about 400 meters from the revered Shiite shrine containing the grave of a granddaughter of the Prophet Muhammad.

The human rights group also reported that two car bombs killed at least 59 people and wounded dozens in the district of Al-Zahraa in the central city of Homs.

IS said online that two suicide bombers struck in Sayyida Zeinab and two others drove explosive-packed cars into crowds in Homs.

UN special envoy for Syria Staffan de Mistura "strongly condemns" the attacks, a representative of de Mistura said in a statement.

Al-Zahraa, whose residents are mostly from the same Alawite sect of Shiite Islam as Syria's ruling clan, has been regularly targeted.

World powers, which have been pushing for a halt to Syria's nearly five-year war, had hoped to see a truce take effect on Friday but have struggled to agree on the terms.

On Sunday, Kerry spoke with Russian Foreign Minister Sergei Lavrov at least three times to try to nail down a truce.

"We have reached a provisional agreement, in principle, on the terms of the cessation of hostilities that could begin in the coming days," Kerry said in Amman, Jordan, after one round of talks.

The Russian Foreign Ministry later said that Lavrov and Kerry held two more telephone conversations and finalized the cease-fire terms to be submitted to their respective presidents.

World powers proposed the truce just over a week ago as part of a plan that also includes expanded humanitarian access, in a bid to pave the way for peace talks to resume.