Assailants have killed a prominent member of the Shia Muslim Houthi delegation to Yemen's reconciliation talks, while an Islamist party's representative has been targeted by a car bomb, according to Yemeni security officials.
Authorities said on Tuesday that Ahmad Sharafeddin died instantly and the assailants escaped.
It was not immediately clear who was behind the assassination, but another Houthi politician, Abdulkarim al-Khiwani, accused Sunni Muslim fighters of carrying out the attack.
Sharafeddin, a law professor, was shot as he drove from his house in Sanaa to the hotel where the talks were being held, a security official said.
He is the second Houthi representative to the talks to be killed since Abdulkarim Jadban, a member of parliament, was shot in a similar attack in November.
The Houthi group fought Sunni Salafis in northern Yemen from October until earlier this month, when a ceasefire was reached to relocate the Salafis to another city 250km away.
However, clashes have continued in other parts of northern Yemen with tribesmen allied to the Salafis.
More than 210 people have been killed in the fighting that erupted in late October after the Houthis accused the Salafis of recruiting foreign fighters in preparation to attack them.
Federal system approved
Tuesday's attack was the latest in a string of killings against prominent Yemenis and foreigners.
Last week an Iranian diplomat was killed in Sanaa when he resisted armed men who were trying to kidnap him.
In another development related to the reconciliation talks, Yemen's political factions extended President Abd-Rabbu Mansour Hadi's term by a year and approved a new federal system on Tuesday.
They gave interim Hadi, whose two-year term had originally been due to end with elections in February 2014, an extra year after delays in the transition to democracy.
He will oversee a shift to a federal system intended to accommodate southern separatist demands for more autonomy.
Southern separatists have been demanding to revive the state that merged with North Yemen in 1990.
The dialogue is part of a transition backed by the UN and the Gulf Arab countries that saw Yemeni President Ali Abdullah Saleh step down after 33 years in power following prolonged protests.