Speaking before talks with Defence Minister Kim Kwan-Jin, Gates said he and Kim would discuss close coordination to deter future provocations.
Washington and Seoul accuse Pyongyang of torpedoing a South Korean warship last March with the loss of 46 lives, a charge it denies.
Tensions rose even higher after the North on November 23 bombarded a South Korean border island, killing four people including civilians.
Kim said the South expects more provocations this year and must respond "from a position of strength". Washington bases 28,500 troops in the South.
"We are all concerned about the tense situation on the peninsula caused by North Korea's continued belligerence and repeated provocations over the past few months," Gates said in a statement before his talks.
The US defence chief said diplomatic engagement with the North is still possible if it takes steps to mend ties with its neighbour.
"With regard to next steps on North Korea, diplomatic engagement is possible, starting with direct engagement with DPRK (North Korea) and the South," he said.
"When or if North Korea's action shows a cause to believe that negotiations can be productive and conducted in good faith, then we could see a return to the six-party talks."
The North quit the aid-for-nuclear disarmament talks in April 2009, a month before staging its second nuclear test. It has expressed conditional willingness to return.
But the US, Japan and South Korea say the North must first improve relations with the South and show a real commitment to scrapping its nuclear arsenal.
Gates began his tour in China and arrived in Seoul from Japan.
In Tokyo Thursday he urged the communist North to take concrete steps to show it is "serious" about talks after Pyongyang offered limited dialogue with Seoul.