Al Houthi rebels have claimed Saudi warplanes have been dropping phosphorous bombs on them, according to agency reports.
"The Saudi air raids resumed this morning. Saudi combat fighter jets launched intense raids against border areas inside Yemeni territory on Sunday night," rebel spokesman Mohammad Abdessalam said.
"The Saudi military used phosphorus bombs during those night raids, burning mountainous regions."
He said that the raids targeted Malaheez, seven kilometres (3.8 miles) inside Yemen, as well as the border villages of Hassameh and Shida and several villages around Jebel Al Dukhan mountain straddling the border.
The Saudi authorities insist that attacks by their forces are limited to targeting rebel locations inside Saudi territory.
However, Riyadh has confirmed it launched reprisals against the Yemen-based Zaidi rebels also known as Huthis after they attacked Jebel al-Dukhan, killing one Saudi border guard and wounding 11 others.
The rebels have also accused the Sanaa military of using phosphorus bombs in Operation Scorched Earth, launched on August 11 against their stronghold in the country's northern Saada province.
Sanaa says its forces do not possess such weapons in their arsenal.
On Saturday President Ali Abdullah Saleh said the campaign against the rebels was only just beginning.
"The real combat only started three days ago," he said.
