U.S. Assistant Secretary of State Kurt Campbell has urged South Korea to exercise patience with regard to U.S. ratification of a South Korea-U.S. free trade agreement.

Campbell, who will visit Seoul early next month, told reporters on Thursday that now is not an appropriate time to discuss when the U.S. will ratify the trade deal, citing other domestic political concerns.

The U.S. official said he is aware that the ratification is very important to the Seoul government but stressed that the Obama administration is currently faced with numerous unprecedented economic challenges.

Meanwhile, Campbell called North Korea's artillery firing into the Yellow Sea "an act of provocation," saying that Washington is continuing to analyze the North's intent behind the move.