Islamic State has released an audiotape it says was recorded by its leader, Abu Bakr al-Baghdadi, days after reports that he had been killed or injured.
In the recording, released via social media, the speaker says IS fighters will never stop fighting “even if only one soldier remains”.
Correspondents say the recording appears authentic and recent.
BBC analysts say the message is probably also intended to counter the claim that Baghdadi has been killed.
The IS leader was said to have been caught in a US-led air strike near the Iraqi city of Mosul last week.
Thursday’s 17-minute recording makes no direct reference to that air strike, but does mention some developments that have occurred since then.
An English transcript of the recording was also released.
Among those are mentions of US President Barack’s Obama decision to deploy an extra 1,500 troops to Iraq – a move announced shortly after the air strike on Mosul.
BBC Arab affairs editor Sebastian Usher says the tone of the recording is characteristically defiant and incendiary, and the cadences and language do sound like those of the Islamic State leader.
The recording calls on IS supporters to “erupt volcanoes of jihad” across the world.
He disparages opponents of IS as “Jews, Crusaders, apostates… [and] devils”, and says the US and its allies “are terrified, weak and powerless”.
The recording also calls for attacks in Saudi Arabia – describing Saudi leaders as “the head of the snake” – and says that the US-led military campaign in Syria and Iraq is failing.
Gulf state rulers, who have joined the US-led coalition against IS, are described as “treacherous”.
There are also new pledges of allegiance from jihadist groups in Libya, Egypt and Yemen that also occurred in recent days.
“O soldiers of the Islamic State… erupt volcanoes of jihad everywhere. Light the earth with fire against all dictators,” Baghdadi says.
“God has ordered us to fight. `For that reason the soldiers of the Islamic State are fighting… they will never leave fighting, even if only one soldier remains. They will never leave fighting, because they reject humiliation.”
Islamic State has seized swathes of Syria and Iraq since June, declaring a caliphate over territory it controls.
Baghdadi himself is a shadowy figure who only showed himself publicly for the first time in a video released in July, delivering a sermon in Mosul, Iraq.
He claims lineage from the family and tribe of the Prophet Muhammad.
Although currently limited to Iraq and Syria, IS has promised to “break the borders” of Jordan and Lebanon and to “free Palestine”.
The group has attracted support from extremists around the world and demands that all swear allegiance to Baghdadi.
Source: BBC