Islamic State (Isis) leader Abu Bakr al-Baghdadi is believed to have released an audio recording calling for attacks against the rulers of Saudi Arabia.
The speech, transcribed in Arabic and translated into English, was posted on the militants' social media feeds.
"O sons of al-Haramayn...the serpent's head and the stronghold of the disease are there...draw your swords and divorce life, because there should be no security for the Saloul," Baghdadi said.
Haramayn is a reference to the two holiest places in Islam, both of them in Saudi Arabia.
Baghdadi also said that the Islamic caliphate established in Iraq and Syria last June is expanding to Saudi territories and that a US-led military campaign against his group was failing.
"We announce to you the expansion of the Islamic State to new countries, to the countries of the Haramayn, Yemen, Egypt, Libya, Algeria," he said.
"Oh soldiers of the Islamic State...erupt volcanoes of jihad everywhere. Light the earth with fire against all dictators."
Referring to US-led military action against his group, Baghdadi said: "Despite this Crusade campaign being the most fierce and severe of all, it is the greatest failure."
"We see America and its allies stumbling in fear, weakness, impotence and failure.
"Oh soldiers of Yemen...be harsh against the Houthis [Shi'ite] , they are infidels and apostates. Fight them and win against them."
Baghdadi also congratulated militant group Ansar Bayt al-Maqdis recently swore allegiance to IS for starting jihad against what he called the "dictators of Egypt". He also urged supporters in Libya, Algeria and Morocco to prevent secular groups from ruling.
The speech was delivered after unverified reports emerged that Baghdadi was wounded during a drone strike attack in the Iraqi city of Mosul.
US State Department spokeswoman Jen Psaki said she could not confirm the recording's authenticity and said Washington and others were likely to increase efforts to counter the group's claims to represent Islam.
"Clearly the brutality, the rhetoric, the efforts to incite, by any leaders of IS ... is not a new phenomenon. It certainly is a reminder to everyone in the region and around the world of what their intentions are," Psaki told reporters.