Residents in Sanaa say warplanes from a Saudi-led coalition have begun attacking targets just hours after a three-day truce in Yemen's war expired.
The airstrikes, which residents said began at dawn on Sunday (local time), were reported over some military sites in Sanaa in the Hafa camp to the east and in the Nahdein area in the south.
Radar positions were also targeted in the Houthi-controlled city of Hodeida and in the contested southwestern city of Taiz, residents reported.
The ceasefire, agreed to allow for an increased flow of humanitarian aid, ended without renewal after a day of heavy fighting between the Saudi-led Arab coalition and the Iran-allied Houthi movement.
Each side accused the other of repeatedly violating the truce and UN attempts to extend it before it lapsed appeared to have failed.
"The [Houthi] coup militias deliberately thwarted the truce and that further convinced our military and political leadership of their unwillingness to accept a peace," the government's army chief of staff Mohammed Ali al-Miqdashi said on Saturday.
Houthi-run TV channel al-Masirah said that pro-Houthi fighters had launched an artillery attack on government forces near Taiz.
A Saudi civil defence spokesman told state news agency SPA that missiles launched by the Houthis from inside Yemen destroyed two houses in the southern Saudi province of Jazan early on Sunday.
The air strikes happened hours before the arrival in Sanaa on Sunday of UN envoy Ismail Ould Cheikh Ahmed, who told reporters at Sanaa airport he would discuss options for a political solution with Houthi representatives and try to secure another ceasefire.
The United Nations and diplomats had hoped a pause in the conflict would pave the way for talks to end a 19-month-old war which has killed at least 10,000 people in the Arabian Peninsula's poorest country.
The coalition has been fighting Houthi rebels and forces loyal to former president Ali Abdullah Saleh in Yemen since March 2015 to try to restore to power the internationally backed President Abd-Rabbu Mansour Hadi, who went into exile.