SANAA, April 7 (Xinhua) -- A scheduled trip of the UN Special Envoy Martin Griffiths to Yemen's rebel-held capital Sanaa on Sunday was delayed, a Houthi official said.

Griffiths was set to arrive in Sanaa on Sunday to discuss the implementation of Stockholm Agreement with the Houthi rebels.

However, a plane arrived earlier the day in Sanaa was carrying other UN officials, the official said on condition of anonymity. He declined to give further details.

The UN special envoy's office could not immediately be reached for comment.

Yemeni warring parties reached a peace deal in December last year in Stockholm as the first step toward ending the four-year-long civil war.

However, the deal has hit a deadlock as the warring forces have largely held the cease-fire deal but failed to withdraw from the port city of Hodeidah.

Griffiths has been shuttling between the rebels in Sanaa and the Yemeni government in the Saudi capital Riyadh to push the deal toward implementation.