The US and the United Arab Emirates are discussing between them the possibility of lifting sanctions against Syrian President Bashar Assad if he walks away from Iran and cuts off arms routes to Lebanon and Hezbollah, five people with knowledge of the talks told Reuters.

The talks have intensified in recent months, the same sources say, in light of the possible December 20 expiration of sweeping U.S. sanctions on Syria and Israel’s campaign against Tehran’s regional network, which includes Hezbollah in Lebanon, Hamas in Gaza, and Iranian assets in Syria.

The talks took place before rebels swept through Aleppo last week in their biggest offensive in Syria in years.

According to the sources, the new rebel advance is an indication of exactly the kind of weakness in Assad’s alliance with Iran that the Emirates and US initiative aims to exploit. But if Assad “embraces” Iranian help for a counter-offensive, that could also complicate matters.

Iranian Foreign Minister Abbas Araghchi visited Syria on Sunday in a show of support for Assad, and UAE President Sheikh Mohammed bin Zayed Al Nahyan spoke by phone over the weekend with the Syrian president about the latest developments in his country.