Unidentified gunmen on Tuesday shot dead a law professor who has been representing Shiite Huthi rebels at Yemen's thorny reconciliation talks, a security official said.
Ahmed Sharafeddin, a leading figure in the rebel group, was gunned down as he drove from his house in the capital Sanaa to the hotel where the talks are being held, the official said.
He was attacked at the Saba roundabout, in central Sanaa, and died instantly, the official added, speaking on condition of anonymity.
Sharafeddin is the second representative of the Huthis to the talks to be killed, after gunmen shot dead MP Abdulkarim Jadban in a similar attack in November.
The killing comes as fighting between Huthis and powerful tribes resumed in Amran province after a series of ceasefires brokered by the government had halted months of battles in several northern areas.
The rebels, whose stronghold is the northern province of Saada, accuse the tribes of backing hardline Sunni Salafists fighting the Huthis in the enclave of Dammaj.
The town in Saada province has been besieged by the rebels for months.
Huthi rebels have been battling the Sanaa government for nearly a decade in Saada, but the clashes with Sunni militants have deepened the sectarian dimension of the unrest.
Fighting that erupted in late October has centred on a Salafist mosque and Koranic school in Dammaj.
The conflict has spread in the northern provinces, embroiling Sunni tribes wary of the power of the Huthis, who have repeatedly been accused of receiving support from Iran.
Yemen's national dialogue is part of a transition backed by the United Nations and the Gulf countries which saw President Ali Abdullah Saleh step down after 33 years in power following massive Arab Spring-inspired protests in the region's poorest country.
It aims to draft a new constitution and prepare for general and presidential elections to replace interim president Abdrabuh Mansur Hadi.