Sana'a, Yemen - Yemen's Interior Ministry said on Wednesday it has expanded the search for six Western hostages and their kidnappers to three provinces surrounding the volatile north-western province of Saada where they were abducted five days ago.

"Security forces in the provinces of al-Jawf, Amran, and Hajjah are now partaking in the search," the ministry said in a statement.

It said police forces have closed all roads leading to Saada to prevent the kidnappers from moving the hostages.

"No place would be excluded in the pursuit of the kidnappers and murderers even if they are in the depth of the earth," the statement added.

It said security bodies were using "every means at their disposal to capture the kidnappers as soon as possible."

Meanwhile, thousands of people took to the streets of Saada on Wednesday to protest the kidnapping of nine foreign aid workers and the later killing of three of the hostages, witnesses said.

They reported two separate demonstrations, one in the provincial capital of Saada and the other protest in the Dhahian town that is controlled by the Shiite rebel group of Houthis, the witnesses said.

Local sources said authorities dispatched hundreds more of police and army troopers backed by military helicopters to Saada as the search continued for a British engineer, a German technician, his wife and their three children, whose fate remains unknown.

The six were kidnapped last Friday along with two German female nurses and a South Korean female teacher while on an excursion in the Gharaz district east of Saada province on the border with Saudi Arabia.

The mutilated bodies of the two German nurses and the Korean teacher were found Monday in a dry river valley in Wadi Nushur, 12 kilometres north-east of Saada. They had been killed with pistols and daggers.

The remains of three victims were transferred to Sana'a by a military helicopter Tuesday ahead of repatriation to their home countries.(dpa)