Satellite imagery appears to show extensive damage to an air base in Syria used by Russian forces following an attack by fighters from the Islamic State group, U.S. intelligence company Stratfor said Tuesday.

The images suggest four helicopters and 20 lorries were destroyed by fire inside the T-4 base, which is also known as Tiyas and is strategically located in central Syria between war-ravaged Palmyra and Homs.

The death toll from a wave of bombings claimed by the Islamic State group in the heartland of Syrian President Bashar Assad's regime has risen to 154, a monitor said on Tuesday.

More than 300 people were also wounded in the Monday attacks in the Mediterranean coastal cities of Jableh and Tartus, some of them critically, the Syrian Observatory for Human Rights said.

More than 148 people were killed Monday in bombings claimed by the Islamic State group in northwestern Syria, the deadliest attacks to date in the regime's coastal heartland.

Seven near-simultaneous explosions targeted bus stations, hospitals and other civilian sites in the seaside cities of Jableh and Tartus, which until now had been relatively insulated from Syria's five-year war.

A Macedonian court on Wednesday sentenced five militants to up to four and a half years in prison after finding them guilty of fighting alongside jihadist groups in war-torn Syria and Iraq.

The tribunal in Skopje found the five men guilty of joining a "foreign army", a court statement said, adding that their sentences ranged from two to four and a half years in jail.

The U.N.'s Syria envoy Staffan de Mistura expressed optimism on Wednesday that the stalled peace talks could resume, but stressed it had to happen in "soon" to avoid losing momentum.

His comments came a day after talks between world powers on ending the five-year conflict failed to make a clear breakthrough in Vienna.

Former Syrian prime minister turned key opposition leader Riad Hijab has told AFP in an interview the forces fighting the regime need "actions, not words" from countries that support them.

He said the opposition urgently required surface-to-air missiles to counter the air strikes carried out by the regime and their Russian allies.

Conflicting claims have been made over the nature of the Israeli strike against an alleged weapons convoy to Hizbullah, reported al-Joumhouria newspaper on Wednesday.

Syrian rebels said that the strike targeted a Hizbullah rockets convoy on the Lebanese-Syrian border on Tuesday.

One of three Spanish journalists released after nearly a year held hostage in Syria by an Al-Qaida-linked group said Monday he feels like he is "walking on air", after being reunited with his family.

Angel Sastre added he was grateful to the Madrid government, a day after flying home with fellow freelance reporters Jose Manuel Lopez and Antonio Pampliega on a Spanish defense ministry jet sent to Turkey to bring them back.

A raid by Syrian security forces on a riot-hit prison in the central city of Hama has failed to end a mutiny involving around 800 inmates, a monitor said Saturday.

Ten guards were taken hostage after the violence broke out on Monday following an attempt to transfer detainees to another prison near Damascus where numerous executions of inmates have been reported.

Syrian security forces on Friday began an assault on a prison in the central city of Hama to end a mutiny estimated to involve 800 inmates, a monitoring group said.