Saudi Arabia has repelled an infiltration attempt at its border by Yemeni Houthi fighters who also shelled two border areas in the kingdom, security sources have said.

Sources told Al Jazeera that Saudi ground troops clashed with Houthi rebels on Sunday in Najran and Jazan, as warplanes belonging to the Saudi-led coalition struck positions belonging to the Iranian-backed fighters along the Yemeni border.

Houthi rebels have fired rockets into Saudi Arabia a number of times, killing both members of the armed forces and civilians.

The cross border violence ocurred as Houthis were forced to retreat from strategic areas in Taiz, Yemen’s third city, as forces loyal to the exiled government continued to take over buildings and bases in the area.

The fighters, who back the exiled president Abd-Rabbu Mansour Hadi, are inching closer to the presidential palace in the city, located southwest of the capital Sanaa, army sources said.

Taiz is regarded as a gateway to Sanaa, which was overrun by the Houthis earlier this year.

The advances by the forces backing Hadi have been aided by weapons and troops from Yemen's Gulf neighbours, as Saudi-led coalition warplanes continue to pound rebel positions.

Troops loyal to Hadi on Saturday announced that they had gained control of Shabwa, the fifth southern province they have taken over in the past month.

Loyalist forces in the south launched an offensive last month against the Houthis, forcing them out of the main southern city of Aden in mid-July. They subsequently retook Daleh, Lahj and Abyan provinces.

Military sources say the coalition has provided Hadi's supporters with modern heavy equipment in recent weeks, including tanks and personnel carriers, as well as Yemeni soldiers trained in Saudi Arabia.

The conflict has cost nearly 4,300 lives since March, half of them civilians, according to UN figures, while 80 percent of Yemen's 21 million people need aid and protection.

Source: Al Jazeera and agencies