South Korea is still cautious about holding summit talks with North Korea on the occasion of Russia's war anniversary event in May, a Seoul official said Thursday.

Both South Korean President Park Geun-hye and North Korean leader Kim Jong-un have been invited to the ceremony to mark the 70th anniversary of the Soviet Union's victory in World War II.

Kim is expected to join the Moscow event but Park has not announced a decision yet.

If both of them attend the ceremony, it would set the stage for another historic meeting between the leaders of the two Koreas amid drawn-out tensions on the peninsula. The two have held two previous summits -- one in 2000 and the other in 2007.

Conservative and progressive forces here are split over whether Park should accept Russia's invitation.

The senior South Korean government official indicated a negative view within the administration.

It's a matter of whether Park can have a "substantive dialogue" when she meets with the North's leader, he told reporters on background.

"The government remains open to an inter-Korean summit any time. But we have said it should be held for a substantive dialogue," he said.

Some people say Park's meeting with Kim, albeit brief, would be of significance itself but "we need to think about how meaningful it would be," he added.

On Pyongyang's protest against the cross-border spread of propaganda leaflets, the official said there is no guarantee of resuming talks even if the South curbs the campaign.

The North has urged the South to prevent leaflet scattering by activists here, which Seoul views as a matter related to the freedom of speech.

The official also stressed the need for developing the so-called Korean Peninsula Trust-Building Process aimed at building mutual trust and paving the way for re-unification.

"The policy represents our will to make ceaseless efforts for a change in North Korea," he said, adding that it takes two to tango.

As to two South Korean men detained in the communist nation on espionage charges, he said that sending a special envoy to Pyongyang for their release is not a realistic option being considered.

He cited the unique characteristics of inter-Korean ties.

Last month, the North said it arrested the two, who entered its territory through China, claiming they worked for the South's National Intelligence Service. (Yonhap)