Houthi rebels in Yemen have held dozens of journalists captive for days at a television station in the capital and a media watchdog has demanded their immediate release.

According to Reporters Without Borders (RSF), the rebels launched rocket-propelled grenades at the headquarters of the Yemen Al Youm TV channel in Sanaa on Saturday before storming the station and holding hostage 41 employees inside.

Three security guards were wounded in the attack, the group quoted diplomatic sources as saying.

"We condemn the violent actions towards journalists by the Houthis, which constitute serious violations of the Geneva Conventions," said Alexandra El Khazen, head of RSF's Middle East desk.

"This hostage-taking is typical of the climate of hostility in Yemen towards journalists who are often targeted in this conflict. We call on the Houthi rebels to immediately release the TV channel's journalists."

The assault and hostage-taking comes amid heightened tensions after forces loyal to former president Ali Abdullah Saleh severed ties with the Houthis, sparking days of gun battles and artillery fire in the capital.

At least 234 people have been killed and more than 400 wounded in fighting in Sanaa since the beginning of the month, the International Committee of the Red Cross (ICRC) said on Tuesday.

Saleh's vehicle was struck by an RPG fire on Monday and he was later shot to death, raising questions about what happens next in the nearly three-year war that has killed at least 10,000 people.

Yemen Al Youm TV is affiliated with the General People's Congress, Saleh's party.

RSF's sources said the journalists were forced to surrender the TV channel's access codes, enabling the Houthis to broadcast their own content.

At least 13 other journalists and media workers are currently held hostage in Yemen by armed groups, including the Houthis and al-Qaeda.

Yemen is ranked 166th out of 180 countries in RSF's 2017 World Press Freedom Index.

The bloody conflict has left impoverished Yemen as the world's leading humanitarian disasters with millions of people facing famine. A Saudi Arabia-led military coalition fighting the Houthis continues to blockade much of the country.

Disease outbreaks are also prevalent with at least 2,000 deaths from cholera and hundreds of thousands of Yemenis stricken.