Yemeni police in the capital Sanaa have killed at least seven Shia Houthi activists after they opened fire on hundreds of protesters attempting to storm the government headquarters, according to a protest organiser.

Al Jazeera's Hashem Ahelbarra, reporting from Sanaa, said there was a "serious escalation" of violence under way in Sanaa.

"More than 50 people were also injured in the clashes. There has also been reports of fighting on the outskirts of the city, which is a very dangerous development."

"The situation is now very delicate in the capital," our correspondent said.  

The rebel activists have been camped out in Sanaa for weeks in a campaign to bring down the government and reverse unpopular fuel price increases.

Fighting has also intensified in the northern al-Jawf province where the government is conducting air strikes against Houthi positions.

The authorities claim a senior rebel commander was killed in one of these raids.