Antonio Guterres will hold meetings with the two Yemeni delegations and will address the closing session of this round of consultations, the UN said in a statement.
The Red Sea port city, controlled by Yemen's Houthi rebels since 2014, is a vital entry point for aid into the impoverished country.
The UN statement comes as Syrian troops, backed by Russia and Iran, surrounded Syria's Idlib province ahead of an expected onslaught against the largest rebel-held zone left in the country.
Syrian President Bashar al-Assad said, on Sunday, that allegations against the Syrian government of carrying out chemical attacks are part of the Western "dictionary of lies", state news agency SANA reported.
The rebel alliance controlling Yemen's capital appeared to crumble as a strongman opposed to the internationally recognised government reached out to a Saudi-led coalition fighting the insurgents.