The United Nations on Tuesday called on the Yemeni government and Houthi rebels to extend a truce that is set to expire in two weeks.

The renewable two-month truce that went into effect in early April has made a "considerable positive impact on the daily lives of many Yemenis," Hans Grundberg said at the end of a closed United Nations Security Council meeting.

"Over the past six weeks, civilian casualties have dropped considerably, fighting has sharply reduced with no aerial attacks from Yemen across its borders and no confirmed airstrikes inside Yemen," Grundberg said.

The official added, however, that he was seeing unconfirmed reports of continuing armed clashes that were causing civilian casualties and urged more efforts to continue de-escalating the crisis.

"I continue to engage the parties to overcome outstanding challenges and to ensure the extension of the truce which is set to expire in two weeks," Grundberg said.

As part of the truce, the first commercial flight in nearly six years took off from Yemen's rebel-held capital Monday and Grundberg said another flight is scheduled Wednesday.

The conflict pits Yemen's Saudi-backed government, officially based in Aden, against the Iran-aligned Houthis.

The Houthis took over Sanaa in 2014, prompting a Saudi-led military intervention the following year and igniting a war that has caused what the United Nations terms the world's worst humanitarian crisis.