Islamic State terror group has vowed to blow up world-famous landmarks such as Big Ben, Eiffel Tower and the White House in an audio broadcast.
The chilling threat was purportedly made during a recording by the group's spokesman, Abu Muhammad al-Adnani. "We will make your lives black and dark," he said. British jihadist Abu Abdullah Britani, 32, who fled the UK for Syria last year, also repeated the warning on Twitter.
Al-Adnani's recording appeared to be an attempt to rally Isis fighters and intimidate international audiences amid setbacks in Iraq.
The Arabic broadcast coincided with Isis accepting Boko Haram's pledge of allegiance to expand its caliphate in West Africa, and listed other cities "we want", from Paris and Rome to Jerusalem and Kabul.
Anonymous hackers have launched the Opisis campaign to close down social media accounts of jihadists like Britani to stop them spreading propaganda. But critics say that would make it harder to trace and arrest the culprits.
Meanwhile, a Turkish news channel has released a video that appears to show a man helping three British schoolgirls on their way to join Isis in Syria. A Haber television said the video was filmed on Turkey's border with Syria by the man, who was later detained by Turkish authorities.
In the video, a man speaking in English appears to tell the British girls they will be in Syria within an hour. The girls - identified by British authorities as Shamima Begum, 15, Kadiza Sultana, 16, and Amira Abase, 15 - traveled from the UK to Turkey last month.
Their journey highlighted the difficulty of halting the radicalisation of young Muslims in the west.
There has been tension between Turkey and Britain over who was to blame for the teenagers managing to sneak into Syria to join the extremist group. Turkey accused Britain of failing to notify authorities in time to prevent them crossing the border.
Turkish news reports say 16 Indonesians, including 11 children, were detained trying to cross into Syria to join Isis and another group of the same size has been reported missing in Turkey.
Shiite militia urged to spare Sunnis in Tikrit
A prominent Iraqi Sunni preacher has urged authorities to prevent Shiite militias carrying out revenge attacks on Sunnis in Saddam Hussein's hometown. The militias are fighting alongside Government forces against Isis extremists in Tikrit.
In his appeal, Sheik Abdel Sattar Abdul Jabbar cited reports of the burning of Sunni homes.
Abdul Jabbar said if the Government failed to stop revenge attacks by Shiite militias, the country would face reignited sectarian tensions - as in 2006 and 2007.
Iraqi forces entered Tikrit for the first time on Wednesday from the north and south. On Friday, they fought fierce battles to secure Qadisiyya, in the northern Tikrit, and lobbed mortars and rockets into the city centre, still in Isis hands. The Iraqis expect to reach the center of Tikrit in two to three days.
The Iranian-backed Shiite militias have had a crucial role in regaining territory from Isis.
US General Martin Dempsey said on Wednesday that as many as 20,000 militiamen may be involved in the ongoing Tikrit operations.