Six people were reported dead on Sunday when a rocket hit near an international trade fair in Syria's capital Damascus being held for the first time in five years.

The Damascus International Fair was once the leading event on Syria's economic calendar but had not been held since shortly after the outbreak of the country's war in March 2011.

The Syrian Observatory for Human Rights, a Britain-based monitor of the war, said six people, including two women, were killed and around a dozen wounded in the rocket fire near the entrance to the fair.

A rescuer speaking to AFP on condition of anonymity confirmed the toll.

A source at a hospital in Jaramana, an area southwest of the capital, told AFP he had seen dead and injured being evacuated from the scene.

There was no confirmation of the toll from officials.

However, state television briefly carried a breaking news alert reporting the rocket fire and saying it had caused injuries, citing its reporters at the scene.

The alert was removed shortly afterwards, and a reporter broadcasting live from the fair interviewed several officials who made no mention of the rocket fire or casualties.

"We were preparing to receive visitors when I heard an explosion... then I saw smoke to the side of the entrance to the exhibition hall," 39-year-old Iyad al-Jabiri, a Syrian working at a textile stand at the fair, told AFP.

Decades-old trade fair

The fair opened on Thursday at the capital's Exhibition City and is scheduled to last 10 days.

It was touted as a sign that work towards rebuilding Syria and revitalising its ravaged economy was getting under way, despite the violence that continues in parts of the country.

Its general director, Fares al-Kartally, said the decision to hold it this year was a result of "the return of calm and stability in most regions" of Syria.

"We want this fair to signal the start of (the country's) reconstruction," Kartally told AFP earlier this week.

While Damascus has been insulated from much of the worst violence of the country's war, several key rebel enclaves remain in the Eastern Ghouta region outside the city.

Fighters in the area have regularly fired rockets into the capital, and government warplanes have frequently carried out devastating raids across Eastern Ghouta.

In recent weeks, much of the area has been quieter after the implementation in July of a "de-escalation zone" covering parts of Eastern Ghouta.

The trade fair dates back to 1954 but was last held in the summer of 2011, months after the eruption of protests against President Bashar al-Assad's government.

Since then, the country has spiralled into a bloody civil war that has killed more than 330,000 people, displaced millions and devastated the economy.

The fair is hosting firms from 23 countries that have maintained diplomatic relations with Damascus throughout the conflict.

Coalition strikes

The United States and European countries, which maintain economic sanctions on the Assad regime, were not officially invited, although a handful of Western companies are attending on an individual basis.

Syria's government has seized large parts of the country from rebels and jihadists in recent months and talk has begun to turn to reconstruction and even the reestablishment of ties with Western nations.

But Assad said Sunday that countries seeking to resume ties or reopen their embassies must end their support for Syria's rebels.

"We are not isolated like they think, it's their arrogance that pushes them to think in this manner," he said in a speech to members of Syria's diplomatic corps broadcast on state television.

"There will be neither security cooperation, nor the opening of embassies, nor a role for certain states that say they want to find a way out (of Syria's war), unless they explicitly cut their ties with terrorism," he added.

Meanwhile the Observatory on Sunday said that at least 18 civilians were killed the previous day in air strikes by the US-led coalition on a jihadist-held village in northeast Syria.

Three children were among the victims, said the Observatory, adding that three Islamic State group jihadists were also killed in the raids on Al-Jezaa in Hasakeh province.