U.S. special representative for North Korea Stephen Biegun talks with South Korea's Special Representative for Korean Peninsula Peace and Security Affairs Lee Do-hoon during a meeting to discuss North Korea nuclear issues at the Foreign Ministry on October 29, 2018 in Seoul, South Korea.

U.S. special envoy for North Korea, Stephen Biegun, urged Pyongyang on Monday to return offers of talks, dismissing leader Kim Jong Un's year-end deadline while highlighting Washington's willingness to discuss "all issues of interest".

Tension has been rising in recent weeks as Pyongyang has conducted a series of weapons tests and waged a war of words with U.S. President Donald Trump, stoking fears the two countries could return to a collision course they had been on before launching diplomacy last year.

Biegun arrived in Seoul on Sunday amid speculation he might try to salvage negotiations by reaching out to North Korea, which has vowed to take an unspecified "new path" if Washington fails to soften its stance before the end of the year.

"The United States does not have a deadline. We have a goal," Biegun told a joint news conference with his South Korean counterpart Lee Do-hoon.

"Let me speak directly to our counterparts in North Korea. It is time for us to do our jobs. Let's get this done. We are here, and you know how to reach us," Biegun said.