Diplomats are trying to ensure a fragile ceasefire in Syria holds, as violations continued to be reported in parts of the country.
ITV News Correspondent Dan Rivers, reporting from Damascus, said a loud explosion could be heard in the east of the Syrian capital on Monday.
Saudi Arabia has accused Russia and the Syrian government of violating the ceasefire which only came into force one day ago.
Speaking at a news conference in the Saudi capital Riyadh, Foreign Minister Adel al-Jubeir claims the respective air forces violated the cessation of hostilities.
He warned there would be a "plan B" if it became clear that Syrian President Bashar al-Assad's government and its allies were not serious about the truce.
"There are breaches of the truce by the Russian air force and the regime and we are now consulting on this matter with the countries of Syria's support group, and I think that the commitment to the truce will be an important indicator of the seriousness of the Syrian regime," Mr Jubeir said.
Danish Foreign Minister Kristian Jensen, also speaking at the conference, called for a "strong alliance" to put military pressure on the Assad regime to help end the war in Syria.
Syrian journalist Humam speaks to ITV News, shining a light on life for those still living within the country's devastated borders.
Despite the ceasefire, ITV News has witnessed airstrikes around Homs and seen shelling in Damascus.
An 86-year-old woman with a broken leg was able to get medical treatment as a result of what is at best a shaky truce.