SANAA/UNITED NATIONS – Four airstrikes by the Saudi-led coalition hit Yemen's northeastern Marib province on Tuesday, Houthi-run al-Masirah TV reported, hours after the Houthis claimed large-scale missile and drone attacks on neighboring Saudi Arabia.

The strikes targeted Al-Jubah district in the southern part of the oil-rich province, al-Masirah said, without immediately reporting casualties or damage. Saudi Arabia has yet to comment on the reported strikes.

Earlier Tuesday, Houthi military spokesperson Yahya Sarea said the group had launched dozens of ballistic missiles and drones at Saudi Aramco facilities in Abha, Najran and Jazan, as well as King Khalid Air Base near Khamis Mushait. He vowed that the group would continue operations "deep inside Saudi territory."

ALSO READ: Yemeni govt says forces destroy Houthi explosive-laden boat in Red Sea

Saudi authorities said the Houthi attacks targeted civilian and economic facilities in Abha, Khamis Mushait, Jazan and Najran, injuring 73 people, including women and children. The Saudi Energy Ministry said fires broke out and operations at some energy facilities were temporarily halted.

The escalation comes as fighting between government forces and the Houthis widens across Yemen. Government forces said Tuesday they had retaken the Al-Yatmah area in the northern province of Al-Jawf, while clashes continued on other fronts, including in western Yemen, where fierce fighting has raged as the Houthis push toward government-held areas near the strategic Bab al-Mandab Strait.

Yemen has been mired in conflict since late 2014, when the Houthis seized Sanaa and much of northern Yemen, prompting a Saudi-led coalition to intervene the following year in support of the internationally recognized Yemeni government.  

UN condemns Houthi attacks

Meanwhile, the United Nations condemns the cross-border attacks by the Houthis in Yemen against multiple sites in southern Saudi Arabia, which affected civilian and energy infrastructure, said Stephane Dujarric, spokesperson for UN Secretary-General Antonio Guterres.

The world body also expresses deep concern over reports of civilian casualties in the attacks, the spokesperson said, adding that the United Nations is equally concerned by the intensification of military clashes across multiple front lines within Yemen, particularly reports of possible civilian casualties resulting from the fighting.

READ MORE: Houthi missile, drone attacks kill 8 on Yemen's western coast

"We call upon the parties to exercise restraint and prevent further escalation, and further urge them to uphold their obligations under international humanitarian law to refrain from directing attacks against civilians or civilian infrastructure, and to take constant care to spare the civilian population, civilians, as well as civilian objects," Dujarric said.

UN Special Envoy for Yemen Hans Grundberg continues engaging directly with the parties with the aim of containing the current escalation and preserving space for dialogue. Continued military escalation risks devastating political, economic and security ramifications for Yemen. The parties should engage constructively with UN-led political efforts, said the spokesperson.

The UN Office for the Coordination of Humanitarian Affairs (OCHA) said an escalation in fighting in Yemen is devastating communities already struggling to survive after more than a decade of conflict.

READ MORE: Houthi group claims drone attacks on Saudi crude oil transport facilities

More than 5,600 households have been displaced across Taiz governorate and southern Al Hodeidah governorate since the escalation in fighting on Thursday. At least 11 civilian casualties have been reported in the last week, including two children killed and nine people injured, said the office.

In Marib governorate, there are reports that shelling struck displacement sites over the weekend, resulting in the deaths of two children and injuries to 15 other people. Shelters have been destroyed and families forced to sleep in the open, it said.

Humanitarians are mobilizing to respond, said OCHA. As of Monday, partners have reached 2,340 households, mainly in Taiz, as well as Marib and Abyan, with emergency supplies. Reaching many people in need remains a major challenge.

The world body urgently needs funding to scale up the response. The humanitarian appeal for Yemen, which requires $2.2 billion, remains just 20 percent funded, said OCHA.

The United Nations calls on all parties to respect international humanitarian law. They must protect civilians, including by allowing them to move to safer areas, and must facilitate unimpeded access for humanitarian relief to reach all those in dire need, said the office.