Outgoing US secretary of state Hillary Clinton has issued a parting warning about Syria’s civil war, accusing Iran of playing an increasingly prominent role in directing the violence.

Clinton said Iran’s involvement heightened the danger of a larger regional conflict drawing in Israel or other neighbours.

“I’ve done what was possible to do,” she told reporters on the eve of her last day in office. But she painted a harrowing picture of a war that could still get worse.

“The worst kind of predictions about what could happen internally and spilling over the borders of Syria are certainly within the realm of the possible now,” she said.

The conflict “is distressing on all fronts”, Mrs Clinton told a round-table of journalists, ahead of John Kerry being sworn in as her successor. Yesterday was her last day as Secretary of State, with speculation rife that she will run for President in 2016.

She pointed the finger primarily at Iran in the Syrian crisis, accusing it of dispatching more personnel and better military material to President Bashar Assad’s regime to help him defeat rebel forces.

Its Lebanese proxy, Hezbollah, is also playing a bigger role in the conflict.

“The Iranians are all in for Assad, and there is very little room for any kind of dialogue with them,” Mrs Clinton said.

She spoke after Syria threatened to retaliate for an Israeli air strike, and its ally Iran warned ominously that the Jewish state would regret the attack.

In a letter to the United Nations secretary general, Assad’s regime stressed its “right to defend itself, its territory and sovereignty” and holding Israel and its supporters accountable.

Clinton declined to talk specifically about Israel’s strike, which US officials described as targeting trucks containing sophisticated Russian-made SA-17 anti-aircraft missiles. The trucks were next to a military research building, and the strike hit both the trucks and the facility, US officials said.

If the SA-17s were to have reached Hezbollah, they would have greatly inhibited the Israeli air force’s ability to operate in Lebanon, where Israel has flown frequent sorties in recent years.

The attack has inflamed regional tensions already running high over Syria’s 22-month-old civil war, and which has already led to deaths in neighbouring Turkey and Lebanon.

In her strikingly candid assessment, Clinton spread the criticism to Russia, which has hindered US-led efforts to set global sanctions against the Syrian regime at the UN Security Council.

US Secretary of State Hillary Clinton laughs before delivering remarks on American leadership at the Council on Foreign Relations in Washington. Photo: Reuters

Sign up to our free newsletters

Get the best updates straight to your inbox:
Please select at least one mailing list.

You can unsubscribe at any time by clicking the link in the footer of our emails. We use Mailchimp as our marketing platform. By subscribing, you acknowledge that your information will be transferred to Mailchimp for processing.