for the first time, the US is considering arming rebel groups in Syria.

America’s toughening stance on the issue follows the reported use of chemical weapons by the Assad regime.

In a press briefing on Tuesday, President Barack Obama warned against “rushing to judgment without hard effective evidence”. However, administration officials acknowledged that the information received so far was sufficient for the Pentagon to prepare options including supplying the rebels with arms.

The Obama administration has been blamed for being slow to react to the rapidly developing situation in Syria and even for downplaying evidence of chemical-weapons use, but a spokesperson for the US National Security Council said this week: “Assistance to the Syrian opposition has been on an upward trajectory.”

Israel has warned that arms supplied to the rebel groups could ultimately be used against Israeli and Western targets.

In another development, Hizbollah leader Hassan Nasrallah made a speech in which he admitted for the first time that members of his movement were fighting alongside Assad’s forces in Syria.

While there have been widespread reports of large numbers of Hizbollah fighters in many areas of Syria, Nasrallah had insisted that they had only entered the country to protect Lebanese citizens living in border towns. But Nasrallah warned of a more robust involvement when he said that “Syria has real friends in the region, and the world, who will not let Syria fall into the hands of America, Israel or Takfiri [extreme jihadist] groups. They will not let this happen.”

Meanwhile, senior Israeli officials have admitted that a lecture by Brigadier-General Itai Brun, commander of the IDF’s Military Intelligence Research Division, in which he announced that Israel believed that Syria had used sarin gas against the rebels, was not cleared first with any civilian official outside the IDF.

“We certainly are not looking to create a dispute here with the US,” said one defence source. “Brun should not have made it look as if Israel is challenging Obama to do something in Syria.”

Israel’s main concern over Syria remains the potential transfer of advanced weapons, including chemical ones, to Hizbollah in Lebanon.

In January, Israel attacked a convoy of advanced anti-aircraft missiles bound for Lebanon, although reports early this week of an Israeli attack on a Syrian chemical weapons base appear to be unfounded.

A large-scale exercise carried out by thousands of reserve soldiers by the IDF in the north of Israel this week fuelled rumours of an operation in Lebanon or Syria, but the exercise had been planned many months in advance.

Israeli officials stressed that, while the IDF would have to act immediately if chemical weapons were being transferred to Hizbollah, the policy is to try to contain the situation in Syria. The chances of succeeding, however, are diminishing by the day.