Saudi-led air strikes have pounded Yemen's capital in one of the heaviest bombardments since the military campaign began.
The raids by coalition forces on Sunday are reportedly part of a major push to retake Sanaa from Houthi rebels, who have held the city for a year.
Al Jazeera's Hashem Ahelbarra said the latest operation "could be a turning point in the fight to recapture the city".
The coalition, as well as forces loyal to exiled President Abd-Rabbu Mansour Hadi, are reportedly "building momentum" as they take an offensive to capture the provinces of Marib and Jawf on the eastern border of Sanaa.
If recaptured, Hadi loyalists are expected to try and seize the capital next.
But our correspondent said that it is only the beginning of a difficult fight.
The Houthi rebels still control Sanaa, a year after they overran it with support from renegade troops still loyal to Hadi's ousted predecessor, Ali Abdullah Saleh.
But they have lost territory in the south since late July when the coalition began deploying ground troops in support of the exiled president's loyalists.
Meanwhile, coalition air strikes also hit a Houthi-controlled security complex in central Yemen, reportedly killing many Houthi rebels, some of them prisoners, witnesses and medics said.
A first strike on the complex in the Ibb province town of al-Qaeda caused no casualties, but a second strike hit as guards were evacuating some 300 detainees, the sources said.
Fifty people were wounded.
A Saudi-led coalition has conducted air strikes on rebel positions across Yemen since March and has provided training and heavy weapons to forces seeking to reinstate the exiled president.
Source: Al Jazeera and agencies