Saudi Arabia has pledged to ensure a stable supply of oil to South Korea, which is under pressure from the United States to reduce purchases from Iran, a report said on Wednesday.

The kingdom also agreed during a visit by South Korean President Lee Myung-Bak to bolster defence cooperation with the east Asian nation.

The assurances over oil supplies came as Lee held talks on Tuesday with Saudi Oil Minister Ali al-Naimi and the head of state oil giant Saudi Aramco, Khalid al-Faleh.

They discussed "means of bilateral cooperation between both countries," Saudi state news agency SPA said without giving further details.

But South Korea's Yonhap news agency quoted a senior official as saying Naimi had "promised to help ensure a stable supply of crude to South Korea."

"Regarding oil supply-demand, we will meet any request and additional demand from South Korea," senior South Korean presidential press secretary Choe Geum-nak quoted Naimi as saying.

"Lee asked for Saudi's support for a stable supply of crude oil to South Korea in case of a contingency, stressing that a rise in oil prices at a time of global economic difficulty could deal a blow to the world economy," Yonhap quoted the official as saying.

Washington wants close ally Seoul to reduce purchases of Iranian crude in line with a US-led drive to sanction Tehran for its suspected nuclear weapons programme.

Naimi said last month that Saudi Arabia was ready to make up for any shortfall in Iran's oil exports under new Western sanctions, an announcement that prompted Tehran to urge Riyadh to "reflect" on its vow.

South Korea, the world's fifth largest oil importer, accounts for around 10 percent of Iran's oil exports but has yet to cut the imports of Iranian oil due to fears of economic damage.

In 2011, top world oil exporter Saudi Arabia exported 270 million barrels of oil to South Korea, accounting for 31.4 percent of Seoul's entire oil imports.

Lee also held talks with Saudi Arabia's defence minister Prince Salman bin Abdul Aziz on Wednesday, according to SPA, which said they discussed "cooperation between the two countries."

But Yonhap quoted Choe Geum-nak saying that officials of the two countries had agreed to conclude a defence cooperation pact possibly in the first half of the year.

Such a cooperation pact could be signed if and when the Saudi minister visits Seoul, the presidential press secretary said. Otherwise, South Korea's Defence Minister Kim Kwan-jin would visit Riyadh for talks, he added.

"The focus of this visit is to lift cooperation in non-economic areas to the level of the economic sector," the official said, according to the Korean news agency. "What is important is that the two sides agreed to elevate defence cooperation as well to match such a level."

Last year, South Korean builders won construction deals worth $16.6 billion in Saudi Arabia.

In mid-November, Saudi Arabia announced that it had signed an agreement with South Korea on developing nuclear power generation to help meet rising demand for energy in the kingdom, Iran's regional arch foe.

Lee will also visit the kingdom's gas-rich neighbour Qatar on Thursday and make a stop in the United Arab Emirates on his way home.

"I am determined to work harder than any other heads of state to overcome the (global financial) crisis this year, including visiting the three Middle Eastern nations," Lee said during a meeting with South Korean residents in Saudi Arabia.