SEOUL (Reuters) -Senior South Korean officials will visit Washington on Wednesday for urgent discussions aimed at finalising a tariff deal that has been on hold over details tied to a $350 billion investment, ahead of an Asia-Pacific summit later this month.

Presidential Policy Secretary Kim Yong-beom and Industry Minister Kim Jung-kwan, who met U.S. Commerce Secretary Howard Lutnick last Friday, will reconvene with Lutnick again to iron out outstanding differences over the large investment pledge.

"Gaps have been narrowed between the two sides on many issues, but there are a couple of matters over which the two sides still stand apart," Secretary Kim said before boarding a flight to Washington.

Kim said he would seek to reach an agreement that is in the interests of both countries and would not sign any partial deal solely to meet a deadline.

South Korean officials have said Washington was no longer insisting on an "upfront" payment of the sum largely in the form of equity, which Seoul has said would destabilise its foreign exchange market.

The security allies have expressed optimism about a breakthrough in the stalled talks as their leaders are expected to meet on the sidelines of an Asia-Pacific Economic Cooperation (APEC) summit later this month in South Korea.

Shares of South Korean automakers Hyundai Motor ( HYMLF ) and Kia Corp ( KIMTF ) rallied on Tuesday on hopes of a trade breakthrough. U.S. tariffs on South Korean cars remain at 25% pending a final deal, whereas duties on other imports have been cut to 15%.