The UN envoy to Yemen Martin Griffiths and the US envoy Timothy Lenderking returned Sunday from Riyadh to Muscat to start a new round of talks with the Houthis on the Saudi peace initiative, while fighting continues on several fronts in the governorates of Ma'rib, Al-Jawf and Taiz.

It is assumed that Griffiths and Lenderking will meet leaders of the Houthi group again in the Omani capital, as part of a diplomatic move to reach a ceasefire agreement that paves the way for a political settlement in Yemen.

The UN and US envoys met with Yemeni President Abd Rabbu Mansour Hadi in the Saudi capital, Riyadh.

Sources told Al-Jazeera that Hadi had reservations about the Houthis ’adherence to the unconditional opening of Sanaa airport and the port of Hodeidah.

During his meeting with the UN envoy Griffiths, the Yemeni president said, "The Yemeni government made many concessions with the aim of ending the conflict in Yemen, but it was met with intransigence and intransigence by the Houthi militia," stressing that the government will continue to deal positively with any initiatives and efforts to bring peace to Yemen.

The Yemeni News Agency quoted Hadi as saying that the continued escalation of the Houthis in Marib and other governorates confirms that they do not intend to devote themselves to peaceful options to end the war.

Before that, sources revealed to Al-Jazeera that the Houthis adhered to the ongoing talks to open Sanaa airport and the port of Hodeidah, as a condition for engaging in ceasefire arrangements as part of a possible political settlement that would end the war.

In the context, sources reported to Al-Jazeera that the Houthi’s previous talks with UN envoy Martin Griffiths were characterized by a degree of flexibility, but they witnessed a complexity regarding the proposal for the simultaneous implementation of commitments.

Alliance battles and raids

On the ground, Houthi media reported that, on Sunday, the coalition forces launched 28 raids on sites in the districts of Sirwah and Meddhal in the Ma'rib Governorate (northeastern Yemen).

Yemeni military and local sources said that violent clashes broke out between the army and the Houthis at the "Kasara" front, northwest of the city of Ma'rib, which the Houthis have been trying for weeks to reach.

The sources added that the army, with the support of the coalition aircraft, was able to retake sites captured by the Houthis.

The clashes led to the displacement of dozens of families from 3 camps for the displaced, as well as injuries and tents burning as a result of the bombing.

In Al-Jawf governorate, which borders Marib, the army said that it had gained control of new sites in the Burt Al-Anan district, in the north of the governorate.

In simultaneous developments, the Media Center of the Yemeni army in the Taiz axis (southwest of Yemen) said that at least 20 militants from the Houthi group were killed on Sunday during battles with the army on the Al-Ahkum front, south of Taiz governorate.

The same source also confirmed the killing of Houthi gunmen during clashes in the "Maqbana" district, west of the governorate.

A military source said that an army soldier was killed and 3 others were injured during the confrontations in the mountains of “Al-Oudin,” “Al-Tawer,” and “Al-Matahen,” and in the Al-Ahkum front, in Haifan district, southeast of Taiz.