Undentified gunmen killed a leading representative of the Shiite Houthi group at the Yemeni national dialogue conference in the capital Sanaa on Tuesday, police said.

Ahmed Sharaf al-Din, a leading figure of Houthi rebels, was gunned down by unidentified gunmen near his home while he was about to drive to the dialogue conference.

"About 15 bullets hit the head and neck of Sharaf al-Din in Tunis Street in downtown Sanaa," one of the police officer told Xinhua.

Yemeni President Abd-Rabbu Mansour Hadi arrived at the conference after the assassination of Sharaf al-Din and he condemned the killing. The representative of the Houthis withdrew from the talk in protest of the killing of their leading figure.

Meanwhile, the United Nations envoy to Yemen Jamal bin Omar condemned the killing of the Houthi representative in a statement issued in the conference being held in Sanaa.

It was the second assassination against the Hiouthi delegates in the national dialogue in less than two months after the killing of Abdulkarim Jadban on Nov. 22.

Houthi rebels have been participating in a UN-backed national dialogue, which started in March and tasked to draft a new constitution and prepare for holding presidential elections.

The government has tightened security in Sanaa since sectarian tensions between the Shiite rebels and Sunni Salafists flare last October in the northern province of Saada, where violence had killed hundreds of people from both sides.

The government brokered a ceasefire agreement earlier this month between the armed rival groups and evacuated around 15,000 Salafi families from Dammaj town in Saada province.

Shiite rebels have controlled the Saada province since they signed a ceasefire deal with the government in August 2010, which ended a six-year intermittent war.