SANAA, Sept. 16 (Xinhua) -- The UN Special Envoy for Yemen Martin Griffiths arrived in Yemen's rebel-held capital Sanaa on Sunday, a week after Geneva peace talks collapsed following the Houthi rebels' absence.

Griffiths appeared well guarded, leaving the plane in a hurry and refusing to speak to journalists. His convoy drove quickly down the city.

Sources told Xinhua that Griffiths immediately met top rebel officials upon his arrival at his residency. The UN envoy's visit to Sanaa aimed to revive the peace efforts, but no further details have been reported yet.

On Tuesday, Griffiths told a Security Council meeting on the situation in Yemen that the war has been escalating across all fronts. "The level of confidence is at its lowest and the human and humanitarian cost is ever rising," he said.

Griffiths' arrival in Sanaa came days after holding intensified meetings with the representatives of the Sunni Saudi-backed Yemeni internationally-recognized government and their foe Shiit Iranian-allied Houthi rebels in neighboring Oman.

Sanaa streets appeared Sunday almost empty of movement due to unprecedented severe shortage of fuel.

Following the collapse of peace talks in Geneva on Sept. 8, the government forces backed by the Saudi-led coalition warplanes advanced into the edges of rebel-held Red Sea port city of Hodeidah.

The forces tightened siege on the city and main roads linking the port with Sanaa, causing a sharp economic crisis on the rebel-controlled northern cities.

Hodeidah port is the entry point of about 70 percent of the country's food, medicines, aid and fuel.

In 2016, a similar UN-backed peace negotiations between the Yemeni rival parties in Kuwait have failed to achieve peace progress after several months of talks.

Yemen has been locked into a civil war since the Houthi rebels overran much of the country militarily and seized all northern provinces, including capital Sanaa, in 2014.

Saudi Arabia is leading an Arab military coalition that intervened in Yemen in 2015 to support the government of President Abd-Rabbu Mansour Hadi after the Houthi rebels forced him into exile.

According to the UN, Yemen is now undergoing the world's worst humanitarian crisis, with an estimated eight million of Yemenis remaining precariously close to famine.

The war has killed more than 10,000 people, mostly civilians, and displaced three million others.

According to a latest statement by the World Food Programme, intensified conflict is worsening the humanitarian situation, particularly in Hodeidah, the key port which is a lifeline for millions in northwestern Yemen.