Militants were gathering Friday for a new attempt to take the Iraqi city of Samarra, home to a revered Shiite shrine whose 2006 bombing sparked a sectarian war, witnesses said.
A major offensive launched by the jihadist Islamic State of Iraq and the Levant and its allies late Monday has overrun second city Mosul and a swathe of northern and north-central Iraq.
Witnesses in the Dur area, between militant-held Tikrit and Samarra, said they saw "countless" vehicles carrying militants south during the night.
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And witnesses in Samarra, just 110 kilometres (70 miles) north of Baghdad, said gunmen were gathering to the north, east and southeast of the city.
A tribal leader said that militants had approached the security forces in the city, asking them to leave peacefully and promising not to harm the Al-Askari shrine.
They also proposed that tribal leaders form a force to protect the shrine and the city's residents, but security forces refused to withdraw, he said.
Militants already mounted two assaults on Samarra, one on Wednesday and one late last week, which were thwarted only after heavy fighting.
The Al-Askari shrine was bombed by militants in February 2006, sparking sectarian conflict between Iraq's Shiite majority and Sunni Arab minority that left tens of thousands dead.