(Updates with details, quotes and background)
SANAA, March 18 (Reuters) - Assailants on a motorbike on Wednesday shot dead one of Yemen's top journalists, Abdul Kareem al-Khaiwani, who is also an activist close to the country's dominant Houthi group, police sources said.
The group's television channel al-Maseerah said al-Khaiwani, who had served as a delegate for the group in a national dialog conference on Yemen's future, was "martyred in a criminal assassination" near his house in the center of the capital Sanaa.
The killing ends a relative lull in bombing and shooting attacks in the capital since the Houthis ousted the government in January.
There was no immediate claim of responsibility, though Sunni Muslim al Qaeda militants have claimed several previous attacks on the Shi'ite Houthis, whom it regards as heretics.
Yemen is torn by a power struggle between the Iranian-backed Houthis in the north and the U.N.-recognized President Abd-Rabbu Mansour Hadi, who has set up a rival seat in the southern port city of Aden with Gulf Arab support.
Khaiwani's editorials were once the scourge of Yemen's veteran autocrat, former President Ali Abdullah Saleh, and he accused the ruler of 33 years of styling his son to succeed him.
Growing closer to the Houthi movement when Arab Spring protests ousted Saleh in 2012, Khaiwani was among several delegates who represented the group at the talks, convened to map out reforms to be incorporated into a new draft constitution before the Houthis captured Sanaa in September.
But the liberal writer earned the ire of activist allies when he backed the group's dissolution of parliament in February - which critics called a coup - but was remembered fondly for his muckraking past.
"He was one of the godfathers of Yemen's tradition of saying no to those in authority," said his friend, Yemeni writer Farea al-Muslimi.
"His death is a new wound in an already bloody experience for Yemen. It's truly depressing and frightening," he added.
Yemen's lively press and civil society has been struck hard by political tension, and rights group Amnesty International last month accused the Houthis of abducting and torturing those opposed to their rule. (Reporting By Mohammed Ghobari and Noah Browning in Dubai, editing by Sami Aboudi and Hugh Lawson)