BEIRUT, Lebanon — For decades, Saudi Arabia has poured billions of its oil dollars into sympathetic Islamic organizations around the world, quietly practicing checkbook diplomacy to advance its agenda.

But a trove of thousands of Saudi documents recently released by WikiLeaks reveals in surprising detail how the government's goal in recent years was not just to spread its strict version of Sunni Islam — though that was a priority — but also to undermine its primary adversary: Shiite Iran.

The documents from Saudi Arabia's Foreign Ministry illustrate a near obsession with Iran, with diplomats in Africa, Asia and Europe monitoring Iranian activities in minute detail and top government agencies plotting moves to limit the spread of Shiite Islam.

The scope of this global oil-funded operation helps explain the kingdom's alarm at the deal reached on Tuesday between world powers and Iran over its nuclear program. Saudi leaders worry that relief from sanctions will give Iran more money to strengthen its militant proxies. But the documents reveal a depth of competition that is far more comprehensive, with deep roots in the religious ideologies that underpin the two nations.

A cable from the Saudi Embassy in Pakistan noting that the president of the International Islamic University of Islamabad had invited the Iranian ambassador to a cultural week on campus.

The documents indicate an extensive apparatus inside the Saudi government dedicated to missionary activity that brings in officials from the Foreign, Interior and Islamic Affairs Ministries; the intelligence service and the office of the king.

Recent initiatives have included putting foreign preachers on the Saudi payroll; building mosques, schools and study centers; and undermining foreign officials and news media deemed threatening to the kingdom's agenda.

At times, the king got involved, ordering an Iranian television station off the air or granting $1 million to an Islamic association in India.

"We are talking about thousands and thousands of activist organizations and preachers who are in the Saudi sphere of influence because they are directly or indirectly funded by them," said Usama Hasan, a senior researcher in Islamic studies at the Quilliam Foundation in London. "It has been a huge factor, and the Saudi influence is undeniable."

While the documents do not show any Saudi support for militant activity, critics argue that the kingdom's campaign against Shiites — and its promotion of a strict form of Islam — has eroded pluralism in the Muslim world and added to the tensions fueling conflicts in Iraq, Syria, Yemen and elsewhere.