Syrian President Bashar al-Assad said third parties including Iraq were conveying information to Damascus about the US-led campaign of air strikes against the Islamic State (IS) militant group in Syria.

In an interview with the BBC broadcast on Tuesday, Assad said there was no direct cooperation with the US, whose air force has been bombing IS in Syria since September as part of a strategy aimed at rolling back the group.

IS has seized wide areas of Syria and Iraq, declaring them part of a cross-border "caliphate." But the US has said Assad cannot be a partner in the campaign against the group, describing him as part of the problem.

The Syrian government is waging its own, separate campaign against IS, including air strikes in areas that have also been struck by the US-led alliance.

It has been widely assumed the Syrian and US armies have conveyed information about the movements of jets using the same air space.

Asked if there was indirect cooperation, Assad said, "That's true, through third parties, more than one party, Iraq and other countries, sometimes they convey a message, a general message, but there is nothing tactical."

Assad said the Syrian government had known about the US-led campaign before it started but did not have details. The US said in September it had informed the Syrian ambassador to the United Nations before the first strikes.

Asked if there was ongoing dialogue via third parties, Assad said, "There is no dialogue. There is, let's say, information, but not dialogue."

Iraqi officials say they have also passed information to the Shiite ­government in Iran about the US-led campaign against IS. Iran is an important ally of Assad.

The US took a strong position against Assad after the uprising against his rule erupted in 2011, saying he should leave power, and has funneled support including limited amounts of military aid to some armed opposition groups.

US officials say they have not relented in their goal of Assad leaving power but, as has been the case for months, they see no policy likely to achieve this at an acceptable cost, and their priority has switched to fighting IS.

As a result, for months they have tacitly lived with Assad staying in power and said that their focus is to combat the group rather than push Syria's president from power.