War between Israel and Iran could be "inevitable" by the end of the Syrian civil war, according to Israeli Prime Minister Benjamin Netanyahu's former national security adviser.

Iran is trying to build "an air base in Syria" and provide additional weaponry to terrorists in Lebanon in an apparent effort to threaten Israel from two directions, according to the Netanyahu ally. This fear has been brewing in U.S. and Israeli circles for years, but the Israelis think the terms of a nascent Syria cease-fire negotiated by the Trump administration, Russia and Jordan exacerbates the danger.

"Israel should take care for its strategic goal and this is to prevent the Iranians and Hezbollah from building launching pads in Syria," Yaakov Amidror, who counseled Netanyahu from 2011 to 2013, told reporters on a conference call hosted by The Israel Project. "If [the Iranians] begin to build infrastructure which might be used against Israel in Syria and will connect this land corridor into Iraq and begin to move materials from this area into Syria, that will make the war inevitable."

U.S. officials in both parties have raised the same concerns. "A permanent Iranian military base in Syria, potentially near the border with Israel or Jordan, would increase Iran's operational capacity to inflict serious damage against two of our closest allies in the region," Rep. Peter Roskam, R-Ill., and Rep. Ted Deutch, D-Fla., wrote in a May letter to Secretary of State Rex Tillerson.

Netanyahu lobbied throughout the talks for Russia and the United States to keep Iran away from Israel's border and said Russian forces ought not to be trusted to police the southern Syria safe zone. But Israeli officials say their position was ignored in the final agreement.

"The agreement as it is now is very bad," an official told Haaretz. "It doesn't take almost any of Israel's security interests and it creates a disturbing reality in southern Syria. The agreement doesn't include a single explicit word about Iran, Hezbollah or the Shi'ite militias in Syria."

Russia and Iran have fought to protect Syrian President Bashar Assad for years, particularly after then-President Barack Obama declined to attack the Syrian regime in 2013 in response to Assad's use of chemical weapons. Tillerson's cease-fire negotiations may have been influenced by the Trump administration's overall determination to limit U.S. military deployments to Syria.

"They picked the best small footprint option that they could for the maximum amount of impact," House Intelligence Committee chairman Devin Nunes, R-Calif., told the Washington Examiner in June. "Meaning: small troop numbers, heavy involvement with our partners. But in the long run, I don't know if that's going to be successful."

Nunes and other lawmakers worry the United States will succeed in defeating the Islamic State in Syria, only to see Iran gain long-term strategic benefits from its decision to partner with Russia in support of embattled Syrian President Bashar Assad. Amidror hinted that Israel might tolerate some sort of Iranian presence in Syria that didn't impinge on Israeli security, but emphasized they will use their "military capability" to "destroy "enemy forces too close to their border.

"If that will not be taken into account by the those who are making those arrangements, the Americans the Russians and others, that might lead the IDF to intervene and to destroy every attempt to build infrastructure in Syria," the retired Israeli military intelligence general said. "We will not let the Iranians and Hezbollah to be the forces which will win from the long and very brutal war in Syria and to move the focus into Israel."