Russian President Vladimir Putin is facing an unwelcome new financial challenge in Syria after the U.S. pullback enabled his ally Bashar al-Assad to reclaim the biggest chunk of territory in the country still outside his control.

The U.S. decision to keep forces in northeastern Syria to guard oil fields denies Assad access to desperately needed funds to rebuild the Middle East state after eight years of civil war. That’s adding to the urgency of United Nations-led talks between the Syrian government and opposition groups in Geneva starting Wednesday, that Putin has said could be “decisive” in settling the conflict.

While agreement is far from certain, the negotiations on constitutional changes could help unlock money from U.S. allies in the Gulf and Europe, which have withheld aid because of Assad’s close ties to Iran and his refusal to loosen his grip on power by making space for opposition groups.

“If we see some political progress there could be more interest in supporting reconstruction,” said Yury Barmin, a Middle East expert from the Moscow Policy Group, a consultancy. At the same time, the Syrian authorities “clearly feel they are winning,” he said.

Russia’s military intervention in Syria since 2015 succeeded in shoring up Assad at a time when he was at risk of being overthrown in a rebellion backed by the U.S. and its allies. The UN estimates reconstruction costs in Syria at $250 billion and the Syrian leadership can’t count on either of its two main backers, Iran and Russia, for significant financing.

Saudi Arabia has softened its demand for Assad’s immediate departure as the Russian role in Syria has grown increasingly dominant and the U.S. presence has reduced. That accelerated when President Donald Trump last month ordered out U.S. troops protecting Kurdish forces in northeastern Syria, leading to a Turkish offensive that forced the Kurds to turn to Damascus for protection by pledging loyalty to Assad. Russia and Turkey struck a deal last week for joint patrols of a border zone in northern Syria.