The Pakistan army is sending a brigade of combat troops to shore up Saudi Arabia’s vulnerable southern border from reprisal attacks mounted by the Houthis in Yemen, according to senior security sources.

The brigade will be based in the south of the Kingdom, but will only be deployed inside its border, the sources told Middle East Eye. "It will not be used beyond Saudi borders," one said.

It is the latest twist in a brutal and devastating two-year war, which has killed more than 10,000 people in Yemen, injured over 40,000 and brought the impoverished nation to the verge of famine.

Both sides have been accused of war crimes and starving civilians trapped in the carnage.

The war was launched by Saudi Arabia and its Arab coalition allies after the Houthis overran Sanaa, the Yemeni capital, and the southern port of Aden and ousted the Saudi-backed president, Abd Rabbuh Hadi.

Increasingly, the Houthis have been retaliating with cross-border missile strikes on targets deep inside the kingdom.

Last month the Houthis claimed to have hit a military camp near al-Mazahimiyah near Riyadh with what they called "a precision long-distance ballistic missile". The Saudis denied the claim.

On 31 January, a missile killed 80 soldiers on a base run jointly by the Saudis and Emiratis on Zuqar island in the Red Sea, according to reports in Arabic media. The Saudis did not confirm nor deny the strike.

In October a missile was shot down about 65km from Mecca, although the Houthis denied targeting the holy city.

#COAS also met Chief of General Staff of Saudi Forces Gen AbdurRehman bin Saleh Al Bunyan.Both agreed to boost mil coop and collaboration-6 pic.twitter.com/xGMfMF3K2X — Gen(R) Asim Saleem Bajwa (@AsimBajwaISPR) December 18, 2016

The deployment of the Pakistani brigade follows a visit by General Qamar Javed Bajwa, the Pakistani chief of army staff (COAS), to Saudi Arabia on a three-day official visit in December last year.

"COAS reiterated Pakistan's commitment to the security and protection of the Holy Mosques and also the territorial integrity of the kingdom," the Pakistani army said in a statement.

"Later, General Qamar Javed Bajwa met chief of general staff of Saudi Forces, General Abdul Rehman bin Saleh al-Bunyan, to discuss military to military relations, defence cooperation and regional security situation.

"Both leaders agreed to boost military cooperation and collaboration."

The area of deployment for the Pakistani brigade is politically sensitive in Islamabad, because two years ago the parliament rejected a request by Saudi Arabia's King Salman for Pakistan to join a "Sunni" coalition to fight the Houthis.

The Houthis, whose tribesmen mostly follow Zaidism, a variant of Shia Islam practised by a minority in northern Yemen, are backed by Iran, although the level of direct support provided by Tehran is disputed.

Parliament debated the deployment for four days, a debate dominated by the fears of further stoking sectarian violence in Pakistan where 20 percent of the population is Shia.

The parliamentary debate also became the target of intense lobbying.

Iran's foreign minister, Javad Zarif, met both Pakistani Prime Minister Prime Nawaz Sharif and the former chief of army staff, Raheel Sharif, as the debate took place.

The Iranians back the Houthis politically, and Saudi Arabia, the US and Australia all say they have supported them militarily as well.

The senior Houthi leaders have been trained by, and their paramilitary structures modelled on, Hezbollah, the Iran-backed Lebanese militia. Advisers from the Islamic Revolutionary Guard Corps (IRGC) have also been involved.

Last year, state-affiliated media in Iran said the Houthis were using Iran-made Zelzal-3 surface-to-surface solid fuel missiles, although they insisted the weapon was produced "indigenously".

Sharif owes his life to the Saudis, who saved him from execution after a military coup which brought Pervez Musharraf to power in 1999.

However, the prime minister’s wish to repay a personal debt to the Saudis was not reciprocated by the Pakistan army.

Generals argued then that they were overstretched with campaigns against the Pakistani Taliban in the North West Tribal Areas.

Since then, however, senior military sources in Pakistan claim to have pushed the Taliban out of Swat valley and North Waziristan.

Parliament however is currently pursuing expanding trade links with Iran. Awaid Leghari, the chairman of the foreign affair’s committee of the National Assembly, recently met Ali Larijani, the speaker of the Iranian Majlis, and Alludin Boroujerdi, the chairman of Iran's foreign policy and security committee in the Islamic Consultative Assembly.

A parliamentary delegation from Islamabad is also due to visit Tehran in May. They will discuss re-opening three border markets, a projected gas pipeline and tourism.

Leghari told Pakistan's Dawn newspaper that both sides, he observed, were now feeling "internal pressures" to engage in a big way for mutual benefit.

"More pressure would have to be exerted from within the economies and people and media," he said.

The deployment would not be the first in relations between the two states. President Muhammad Zia ul-Haq deployed an elite Pakistani armoured brigade to the kingdom at the request of Fahd, who was Crown Prince and acting monarch at the time of the Iranian revolution in 1980.

The brigade was deployed for a decade and some 40,000 soldiers served in it.

This article is available in French on Middle East Eye French edition.