Al-Harth, Saudi Arabia - The Saudi military is boosting security along the Yemeni border, moving in tanks, artillery units and border guards to counter the threat posed by Houthi fighters.

The extra troops and equipment have been dispatched to the country's southwestern border adjacent to the northern Yemeni province of Saada, the main stronghold of Houthi fighters.

Al Jazeera's Mohamed Vall, reporting from the Saudi side of the frontier on Tuesday, said he saw a convoy of tanks and armoured personnel carriers head towards a mountain range that marks the divide between the countries.

Analysis: Al Jazeera's Mohamed Vall
The Saudi-led campaign against the Houthis is nearly completing its third week without major breakthroughs. 

The rebels have been able to even extend the territory under their control. They are still holed up in parts of the southern city of Aden.

Until now the coalition has only used air power in its bid to take out the Houthis' ground-to-air missile capabilities, destroy heavy weaponry and disrupt supply routes.

Talk of a possible ground invasion never ceases. Several Arab countries have expressed readiness to contribute ground troops.

But a ground invasion needs a political decision by Saudi Arabia's King Salman and careful assessments of the risks involved.

Yemen’s terrain is mountainous. The rebels know it in detail - much better than any foreign army - and for the moment, the chances of a swift victory for the coalition in a ground operation look slim.

The deployments come nearly three weeks into a Saudi-led offensive against the Houthis, who have taken control of large parts of the country and forced President Abd-Rabbu Mansour Hadi to flee the country.

"It's very clear that Saudi Arabia is not willing to take any chances in this war ... one of their main objectives of the campaign is to make sure that it is not affected by the conflict," our correspondent said.

Three Saudi soldiers were killed by Houthi mortar shells in the border area of Najran on Saturday, a military spokesman said.

The Saudi army says it does not yet have orders to chase the attackers beyond the border.

"We deal with them from a distance. We make sure to spot them before they get close and before they can shoot," a commander told Al Jazeera.

"We have an advantage being able to shoot them from a longer range. We rely on information that we collect through various means including goggles and other types of surveillance."

In 2009, Houthi rebels were able to infiltrate the border and inflict heavy casualties on Saudi troops.

In the recent escalation of fighting, the UN has warned of a growing humanitarian crisis in the country, and said the ongoing conflict is taking a heavy toll on civilians.

"Over 600 people [have been] killed, but more than half of them are civilians. This is particularly concerning," Ivan Simonovic, UN's deputy secretary-general for human rights, told Al Jazeera on Monday. 

The Saudi army says it is taking precautionary measures in order not to harm civilians, but with densely populated areas on both sides of the border, the risk of civilian casualties is high should fighting intensify in the area. 

Riyadh says it will not stop air strikes until Hadi is reinstated.

The UN Security Council  on Tuesday approved a resolution effectively imposing an arms embargo on the rebels.

Soldiers have been deployed on the border with Yemen's Saada, a Houthi stronghold [Jamil Bassil/Al Jazeera]
The security deployment comes three weeks into a Saudi-led offensive against the Houthis [Jamil Bassil/Al Jazeera]
Several border villages were abandoned during 2009 fighting, and residents permanently relocated [Mohamed Vall/Al Jazeera]
Tanks, artillery units and border guards have been deployed to the border area [Jamil Bassil/Al Jazeera]

Source: Al Jazeera