TEHRAN, Iran — Senior UN investigators are in Iran for a new round of talks with government officials over allegations that Tehran may have carried out tests on triggers for atomic weapons.

Iranian state TV said Wednesday that talks with the International Atomic Energy Agency could be extended beyond the day, “if necessary.”

The visit by the UN team, led by Herman Nackaerts, comes a day after Tehran raised prospects that the IAEA may be allowed to inspect Parchin — a military site where the agency suspects nuclear-related experiments were conducted — if certain conditions were met.

However, IAEA director general Yukiya Amano said on Monday that “the outlook is not bright” for a Parchin visit, according to the New York Times.

Nackaerts said that “differences remain but we will work hard to try to resolve these differences,” according to Iran’s state-run IRNA news agency.

Iran denies any testing activity at Parchin and insists the facility is a conventional military site only. The possibility of Iran nuclear tests came under greater scrutiny this week, after North Korea successfully tested a nuclear device on Tuesday, setting off a wave of international condemnation. North Korea and Iran and believed to have shared nuclear technology.

The US and its allies fear Iran is seeking to develop nuclear weapons. Tehran denies the charge, saying its nuclear program is only for peaceful purposes.