Investment deals, oil market bonhomie and the Syrian war will dominate landmark talks between the leaders of Russia and Saudi Arabia on Thursday that are set to solidify a deepening relationship between the two energy powers. A delegation to Moscow, led by King Salman bin Abdulaziz, will sign more than $3bn worth of deals between Saudi and Russian energy companies, officials said. It is the first trip to Russia by a Saudi monarch and reflects a new-found friendship between the world’s largest crude exporters that underpins a global agreement which has helped prop up oil prices.  A relationship previously marked by mutual distrust has been replaced during the past year by strategic co-operation bound by economics, trade and geopolitics. Ties between the countries have warmed as Moscow’s relations with the west have deteriorated, and as its influence in the Middle East has risen following its intervention in the Syrian conflict.  “Previously, our relations with Saudi Arabia used to be just on the surface, but right now they are developing rapidly,” Russian president Vladimir Putin said on Wednesday. “There is very good potential, and we are looking ahead with confidence, both with Saudi Arabia and the Middle East in general.” The linchpin of the friendship is a deal struck in December last year by Moscow and Riyadh for a cut in crude production by Russia and the Saudi-led Opec cartel, which helped drag the oil price up above $50 a barrel, easing pressure on both countries’ oil-dependent budgets.  Alexander Novak, Russia’s energy minister, told the Financial Times that there was “a large pipeline of co-operation projects to be discussed far beyond our joint [oil market] stabilisation efforts”. The talks between Mr Putin and King Salman will also focus on Syria, where Moscow and Riyadh have backed rival sides in the conflict, and the wider Middle East.