At least 40 people were killed and dozens more wounded in a series of coordinated explosions across the country, Syrian state media reported.
The blasts happened in government-held areas of Damascus, Homs and Tartous, as well as at a Kurdish checkpoint in Hassakah.
ISIS claimed responsibility for the attacks, according to a statement by the ISIS-affiliated Amaq agency.
Of those killed, 30 died in two explosions on a main highway bridge near Tartous, on the Mediterranean coast.
Another four people died when a car bomb exploded at an army checkpoint in the government-held al-Zahraa neighborhood in Homs, according to Gov. Talal Barazi.
A jeep carrying six suspected militants blew up after a soldier stopped the vehicle on a highway near Damascus. The soldier was killed. Police Gen. Jamal A-Bitar told Syrian TV he believes the car was on its way to carry out an attack in the capital.
And in the Kurdish-controlled northeastern city of Hassakah, a suicide bomber on a motorcycle killed five Kurdish security forces at a checkpoint.
US, Russia talks on Syria
The blasts come as high-level talks between the United States and Russia aimed at ending violence in Syria ended without an agreement, a US official said Monday.
The meeting between US Secretary of State John Kerry and his Russian counterpart Sergey Lavrov on the sidelines of the G20 summit in Hangzhou, China, failed to resolve differences and left the Syrian question unanswered, the official said.
Later in the day, US President Barack Obama and Russian President Vladimir Putin also met for an additional discussion on Syria. The leaders directed Kerry and Lavrov to reach an agreement in the coming days, according to a senior White House official.
Turkey clears ISIS from Syrian border
Meanwhile, Turkey is claiming success
in its campaign to eradicate ISIS from its border regions.
The terror group has reportedly lost control of the last strip of its territory along the Syrian-Turkish border, according to sources and the Turkish state-run news agency Anadolu.
The border town of Jarablus, which Syrian rebels and Turkish forces recently recaptured from the terror group, is a critical location for supplies, money and fighters coming in and out of ISIS-held areas.
Azaz is another key border city that was formerly held by ISIS.
The developments would be a major setback for ISIS, choking off supply lines for the terror group.