The U.S. ambassador to South Korea said Tuesday that Washington is not concerned about the "speed or scope" of inter-Korean dialogue, signaling that its tough stance on North Korea doesn't conflict with Seoul's move to improve ties with Pyongyang.

The remarks by Mark Lippert, Washington's ambassador to Seoul, came amid growing concerns here that Washington's recent sanctions on the North may hamper Seoul's initiative. Earlier this month, the U.S. imposed fresh sanctions on North Korea following the North's alleged hacking attack on Sony Pictures.

"We do not have concerns with the speed or scope of the inter-Korean dialogue as proposed by President Park (Geun-hye). We are quite comfortable and there is no daylight between us," Lippert said in an interview with a group of reporters.

Lippert, 42, said that Seoul seems to be ready to dialogue with the North unconditionally, but North Korea is putting "conditions and caveats" on the resumption of the inter-Korean talks.

"In the case of North Korea, what you don't have is a serious interlocutor on the other side of the table. You've seen most recently conditions and caveats to resume the inter-Korean dialogue," he added, when asked about a difference between North Korea and Cuba.

The ambassador said that the U.S. is still open to dialogue with Pyongyang, but the ball is in North Korea's court as it should show sincere commitment toward denuclearization.

 "When North Korea is ready for credible negotiations leading to complete, irreversible and verifiable denuclearization of the Korean Peninsula, (the U.S.) administration stands ... ready to engage in dialogue," Lippert said.

Touching on frayed Seoul-Tokyo ties, the U.S. envoy said that the U.S. will not play a mediator role between South Korea and Japan, but it will "encourage" the two sides to have further talks to explore improvement in their relations.

 "Our role is not to mediate but to encourage two great nations with two democratically elected leaders to come to a resolution on this."

He expressed hope that dialogue between Seoul and Tokyo, including the sex slavery issue, could produce a satisfactory conclusion that could help the bilateral ties move forward in a "more robust fashion."

This year marks the 50th anniversary of the normalization of diplomatic ties between Seoul and Tokyo and it also marks the 70th anniversary of Seoul's liberation from Tokyo's 1910-45 colonial rule.

The two countries hope to mend their strained ties this year, but Japan's refusal to sincerely apologize over its wartime atrocities, such as its coercion of Korean women into sex slavery, has been the main stumbling block.

Lippert said that the matter of so-called "comfort women" is a "tough and very emotional" issue, saying that the U.S. remains supportive of previous Japanese governments' apologies for the sex slavery and its colonial rule.

 "We continue to have expressed support for the Kono Statement and the Murayama Statement as well and continue to believe that those are important statements that undergird the issue," he said.

Lippert's remarks came amid growing concerns that Japanese Prime Minister Shinzo Abe may issue a new statement that doesn't include Tokyo's apology over its wartime wrongdoing in August to mark the 70th anniversary of the country's defeat in World War II.

Abe said last week that he would not use key words from Japan's previous apologies for its wartime atrocities in his new statement.

Japan issued two key statements containing apologies for past wrongdoing -- the 1993 apology on the sex slavery issue, named the Kono Statement, and the 1995 apology for Japan's colonial rule, named the Murayama Statement.

Lippert assumed the post in late October 2014 as the youngest U.S. ambassador to South Korea. He has pledged to make efforts to deepen and broaden the Seoul-Washington alliance. (Yonhap)