South Korean authorities told the BBC that its foreign minister Kang Kyung-wha spoke to her North Korean counterpart Ri Yong Ho on Sunday on the sidelines of a forum in Manila.
Tensions have escalated on the Korean peninsula in recent months amid repeated missile tests by the North.
The UN Security Council voted on Saturday to impose fresh sanctions.
South Korea proposed talks with the North last month to ease tensions and resume reunions of families separated by the Korean War, but Pyongyang has yet to officially respond.
South Korean media reported that Ms Kang and Mr Ri shook hands in a brief and unarranged meeting at an official dinner event held by the Association of Southeast Asian Nations (Asean).
A South Korean foreign ministry official confirmed the meeting to the BBC.
South Korean news agency Yonhap reported Ms Kang as saying that Mr Ri’s rejection appeared to be connected with mounting sanctions on North Korea.
“I told him that [the two offers for talks] are an urgent matter that should be carried out immediately with any political agenda put aside and asked him to proactively react,” she was quoted as saying.
The foreign minister of China, which is Pyongyang’s closest ally, told journalists on Monday: “My feeling is that the North did not entirely reject the positive proposals raised by the South.” Wang Yi added that China also supported the South’s initiatives.
All three countries’ ministers are attending the Asean forum in Manila
The US Secretary of State Rex Tillerson is also at the forum, where he spoke about North Korea.
He told journalists that the unanimous vote by the UN Security Council to impose new sanctions was “quite clear in terms of being no daylight among the international community” on their desire for North Korea to stop its tests.
He also made a note of Russia and China’s participation in the vote.
The two countries have previously differed with others on how to handle Pyongyang, but in recent months have joined in calls for North Korea to stop its missile tests while also urging the US and South Korea to halt military drills.
On Monday, US President Donald Trump spoke to his South Korean counterpart Moon Jae-in over the phone about relations on the Korean peninsula.
They agreed that North Korea “poses a grave and growing direct threat” and the two leaders were committed to fully implement the latest round of UN sanctions, the White House said in a statement.