Israel opposes arming Syrian rebels unless they are carefully vetted beforehand, Jerusalem’s ambassador to the US said Wednesday.

Michael Oren’s comments to CNN come as the US and other Western countries are weighing upping their involvement in the Syrian civil war after two years of bloody fighting and recent reports of chemical weapons use by the regime of Syrian President Bashar Assad.

“If it were decided to provide lethal assistance, we ask that those groups be carefully vetted,” Oren said. He added that Israeli officials had discussed the matter with their American counterparts.

Israel has expressed worry over Islamist elements among the ranks of Syrian rebels, with some fearing the creation of a jihadi terror base at Israel’s doorstep should Assad fall.

Turkey and Jordan have expressed similar concerns over arming rebels, according to CNN.

Jabhat al-Nusra, or the Nusra Front, an al-Qaeda in Iraq affiliated outfit, has taken a growing role in the fight against Assad, leading to worries among Western officials over the makeup of the rebel groups battling Assad.

In May, France backtracked from its call to end an arms embargo on Syria in order to arm rebels, over fears weapons could end up in the wrong hands, according to French President Francois Hollande.

In January and February, video surfaced of Nusra Front fighters nearing the ceasefire line with Israel on the Golan Heights. In one video, the jihadis say they will acquire Assad’s chemical arsenal for use against Israel.

“We will attack and take over those sites and then use them against the Zionists, from Syrian territory, until we reach Jerusalem,” one fighter says in the video.

An unnamed US official told CNN that Washington had done some vetting of groups in Jordan and Turkey, but only for the receipt of non-lethal aid and training.

Though US officials said last week that they believed chemical weapons had been used in Syria, they have indicated that they will not up their involvement without fully assessing the situation.

However, on Tuesday, US officials indicated that they were looking to increase their support for Syrian rebels.

“Our assistance to the Syrian opposition has been on an upward trajectory.” National Security Council spokeswoman Caitlin Hayden said. “The president has directed his national security team to identify additional measures so that we can continue to increase our assistance.”

Britain has also called for the arming of Syrian rebel groups.