SEOUL - South Korea's Hyundai Engineering & Construction and Hyundai Engineering have signed a $2.4 billion contract with oil giant Saudi Aramco to build a gas processing plant, Seoul's presidential office said on Tuesday.

The deal was signed on Monday in Riyadh at a ceremony to mark 50 years of construction cooperation between the two countries, with South Korean President Yoon Suk Yeol attending as part of his state visit to the kingdom.

The two builders, affiliates of Hyundai Motor Group, have been working on the first phase of Aramco's Jafurah gas processing facilities project after winning the order in 2021, Hyundai said in a statement confirming the signing of the $2.4 billion contract on the second phase.

Jafurah is Saudi's largest unconventional non-oil associated gas field, with reserves estimated at 200 trillion cubic feet (5.7 trillion cubic metres) of raw gas. Aramco has said daily output could reach around 2 billion cubic feet by 2030.

Yoon and Saudi Crown Prince Mohammed bin Salman welcomed the agreement in a joint statement after talks, pledging further cooperation in construction and infrastructure, including on Saudi Arabia's NEOM mega-city and Vision 2030 reform plans.

The joint statement also called for greater efforts to prevent the escalation and spread of the conflict between Israel and Hamas, and urged both sides to stop targeting civilians and allow the "rapid and unimpeded delivery" of humanitarian aid.

State-run Korea National Oil Corp also clinched a storage deal with Aramco during Yoon's visit that allows the Saudi company to store 5.3 million barrels of oil in South Korea's reserve facilities in the port of Ulsan for five years.

After a four-day stay in Riyadh, Yoon left for Doha on Monday where he will attend an international horticultural expo before holding a summit on Tuesday with Qatar's Emir Sheikh Tamim bin Hamad al-Thani, his office said.

(Reporting by Hyonhee Shin; Editing by Tom Hogue)