SEOUL (Reuters) - South Korea and Vietnam agreed on Monday to expand economic cooperation after a ministerial meeting on Monday, at a time when the two countries are racing to mitigate the impact of potential U.S. tariffs.

South Korea's industry minister Ahn Duk-geun is visiting Vietnam as the two countries scramble to negotiate a reduction of threatened U.S. tariffs of 25% and 46%, respectively, that would otherwise apply in July after a global moratorium expires.

Korean companies are the biggest foreign investors in Vietnam, and the Southeast Asian nation is South Korea's No. 3 export destination.

The two countries agreed on action plans to ensure they can meet an existing target to reach $150 billion in bilateral trade by 2030 and cooperate in the generation of nuclear energy and LNG power and investments in the textile and clothes industries, according to a statement from South Korea's industry ministry.

The agreement came during a meeting of Ahn and Vietnam's Trade Minister Nguyen Hong Dien in Hanoi.

Ahn also met with representatives of top South Korean companies, including Samsung Electronics, LG Electronics, Hyundai Motor and HS Hyosung. The minister pledged that Seoul will continue talks with both the U.S. and Vietnamese governments to minimise the impact of U.S. tariffs on Korean companies.

Samsung produces more than 60% of its phones sold globally in the country. Led by national champions such as Samsung, Korean companies have been building their presence in Vietnam for years as the costs of manufacturing in China rose along with political risks and competition.

Now, that reliance on Vietnam threatens to backfire as the looming steep tariffs exposed the vulnerability of the Southeast Asian country's export model.

China's President Xi Jinping also on Monday called for stronger ties with Vietnam on trade and supply chains amid disruptions caused by U.S. tariffs, as he kicked off a three-nation trip to Southeast Asia in Hanoi.

(Reporting by Hyunjoo Jin; Editing by Ed Davies)