The jihadists who have declared a Muslim "caliphate" in parts of Syria and Iraq call themselves the Islamic State but detractors say they represent neither Islam nor any state.

In a speech outlining his strategy against the group on Wednesday, President Barack Obama pointedly denied the extremists their chosen appellation.

Syrian rebels and jihadists from the Islamic State have agreed a non-aggression pact for the first time in a suburb of the capital Damascus, a monitoring group said on Friday.

The Syrian Observatory for Human Rights said the ceasefire deal was agreed between IS and moderate and Islamist rebels in Hajar al-Aswad, south of the capital.

U.S. Secretary of State John Kerry arrived in Ankara Friday for talks aimed at building a coalition against Islamic State jihadists, a visit that comes after Turkey said it would not allow its air bases to be used for strikes on the extremists.

The top U.S. diplomat, touring the Middle East to establish a coalition of more than 40 countries, was meeting with Turkey's leaders including President Recep Tayyip Erdogan for talks on measures to defeat the militants in Iraq and Syria. 

Syria must be part of the coalition against jihadists because the country is a key victim of "terrorism", an adviser to President Bashar Assad said on Friday.

"Terrorism didn't start in Syria today, it started four years ago" when the uprising against Assad began, Buthaina Shaaban was quoted as saying by state news agency SANA.

The Qatari government said it helped to secure the release of 45 Fijian peacekeepers kidnapped by al-Qaida linked Syrian rebels on the Golan Heights last month.

Syrian government air raids on a rebel-held area near Damascus killed 42 people, including seven children, a monitoring group said Friday, giving an updated toll.

Thursday's air strikes were carried out in Douma, a satellite suburb northeast of the capital that has been under siege for more than a year.

Progressive Socialist Party leader MP Walid Jumblat has rejected the so-called self-security, reiterating his warning from the rise of terrorist threats in Lebanon and inquiring the U.S. about planned airstrikes against jihadists in the region.

“Self-security leads to total chaos,” Jumblat warned in remarks published in As Safir newspaper on Friday amid reports that certain Lebanese factions were arming themselves to confront terrorists.

The Australian government on Friday elevated its terrorism threat level to the second-highest warning in response to the domestic threat posed by Islamic State movement supporters.

Prime Minister Tony Abbott announced the increase from "medium" to "high" on a four-tier scale on the advice of the Australian Security Intelligence Organization.

Jubilant Fijians celebrated Friday the release of 45 U.N. peacekeepers from the South Pacific nation who were kidnapped by al-Qaida linked rebels on the Golan Heights, hailing them as heroes after their two-week ordeal.

Fijian leader Voreqe Bainimarama said the prayers of the deeply religious South Pacific nation had been answered with confirmation that fighters from the al-Nusra Front had released the Blue Helmets unharmed.

Islamic State militants in Iraq and Syria now have about 20,000 to 31,500 fighters on the ground, the Central Intelligence Agency said Thursday, much higher than a previous estimate of 10,000.