Sana'a, Yemen  - Army troops battling Shiite rebels in north-western Yemen have killed three prominent rebel field leaders and wounded another in assaults against their strongholds, a military source said Friday.

The source, quoted by the state news agency Saba, said they were killed Thursday when army units attacked rebel positions in al-Malahid district of the war-wracked Saada province, the scene of a massive military offensive on the rebels, who are known as Houthis.

Army forces have been pounding rebel bases in Saada on the border with Saudi Arabia since August 11. The offensive has included aerial, artillery and missile strikes on rebel strongholds in strategic heights overlooking the Saudi border.

Scores of insurgents, civilians and troops have been killed in the past two weeks and around 150,000 people have been displaced.

The military source identified the slain commanders as Jarallah Muhammed Ismail, Ali Abdu-Rabu Jabal and Abdul-Aziz al-Arimi and said a fourth rebel commander, Hussein Yahya Hanash, was wounded.

Saba quoted the unnamed source as saying the army had begun using special force snipers to take down rebel fighters, resulting in "huge losses" for the guerillas.

Commandos were also waging gun battles late Thursday with rebel fighters hiding in houses in the old city of Saada near the provincial capital of Saada, which has the same name, local officials told the German Press Agency dpa.

In the Dammaj area near Saada city, the army destroyed trucks carrying weapons and food for the rebels, who have been sporadically fighting the government since 2004, Saba said.

Authorities accused the Shiite group of seeking to restore the rule of the Zaydi royal family, known as the imams, who were toppled by a republican revolution in northern Yemen in 1962.

The Houthis said they are revolting against government corruption and the Yemeni alliance with the United States.

It was not possible to independently verify the army's reported successes as journalists are denied free access to Saada, about 240 kilometres north of the national capital, Sana'a.

On Thursday, the army reported progress in wiping out bases of the rebels and killing 11 insurgents as government forces destroyed several rebel mountain posts in the districts of al-Minzala, al-Hamazat and Nushur and captured five other posts in Dhu Sulaiman village.

The rebels vowed Wednesday to wage a "war of attrition" after the government dismissed their offer of a ceasefire.

The government rejected the proposal, saying the Houthis should comply with a ceasefire plan that the government set out two weeks ago if they want the fighting to stop.

Conditions of that ceasefire included the withdrawal of insurgents from all districts of Saada and mountainous sites and the surrendering of military hardware seized from the army.

The government also called for the rebels to clarify the fate of a German family of five and a British engineer taken hostage in Saada in June.

The six people were among a group of foreign hostages - seven Germans, a Briton and a South Korean. Three of the hostages - two German women and a South Korean woman - were found dead two days after the abduction. (dpa)