A leader of a Sunni Arab tribal council which opposed al-Qaeda in Iraq has been killed in a roadside bomb attack north of Baghdad, Iraqi officials have said.
Sheikh Muawiya Jebara, a senior member of the Salahuddin Awakening Council, and three of his bodyguards were killed as his convoy travelled near Samarra.
His death comes less than a month after the killing of the head of a similar group in neighbouring Anbar province.
Meanwhile, the Shia mayor of Iskandariya died in a separate bombing.
Abbas al-Khafaji, a member of the Supreme Iraqi Islamic Council (SIIC), and four of his bodyguards were killed when a roadside bomb exploded near their car at a checkpoint, police said.
A mixed Sunni-Shia town 40km (25 miles) south of the capital, Iskandariya lies in a centre of the Sunni insurgency known as the "triangle of death".
The attack on Sheikh Muawiya Jebara occurred in mid-afternoon as he travelled to an area south-west of Samarra to support other members of the Salahuddin Awakening Council who were currently fighting al-Qaeda in Iraq.
The sheikh survived the initial blast, but died from head injuries shortly after arriving in hospital, his brother said.
The head of the Tikrit-based Salahuddin Awakening Council, Sheikh Sabah Mutashar al-Shammari, recently said the tribal alliance had conducted more than 100 operations against Sunni extremist militants.
"Our forces are working in co-ordination with the ministers of defence and interior," he told the AFP news agency.
"Our troops consist of 3,000 fighters distributed across seven headquarters in the province."
Last month, the leader of the Anbar Awakening, Sheikh Abdul Sattar Abu Risha, was killed in a bomb attack near his home in Ramadi.
US officials have pointed to the formation of the tribal alliances as one of the most positive developments in their efforts to reduce violence in Iraq.
In other news, the US military said it had taken an Iraqi member of parliament into custody after he allegedly attended a meeting of suspected al-Qaeda members.
The MP was seized during a joint raid by US and Iraqi forces in the town of Sharqat, north of Baghdad.
The main Sunni Arab alliance in parliament, the Iraqi Accord Front, said the man was one of its members, Naif Jassim Mohammed.
The US military said the man was being questioned by the authorities, but was not formally considered to be a detainee.
Later, parliament agreed to let the Iraqi Accord Front replace another of its MPs with one of the country's most famous football stars.
Ahmed Radhi, the only Iraqi player to have scored in the World Cup, replaced Abed Nasser al-Janabi, who was expelled from parliament in June after saying he was leaving politics to join the insurgency.