Saudi Arabian troops have crossed into northern Yemen for the first time since the conflict with Houthi rebels began in March.
Footage published on Wednesday showed soldiers taking positions in a mountainous area overlooking the southern Saudi province of Jizan.
Houthi shelling and rocket attacks on the border have killed dozens of Saudi soldiers, including a general on Sunday.
Saudi commanders insist the incursions are temporary.
A Saudi-led coalition has launched air strikes at rebel positions in Yemen but the the Houthis and their allies, soldiers loyal to the former president, Ali Abdullah Saleh, insist they are still a capable fighting force.
The Houthis have posted video online of what they say are rebel commandos storming a Saudi border post.
The video shows the fighters capturing the building after heavy fighting and blowing up military vehicles, only to withdraw when Saudi fighter jets launched an air raid in the area.
In July, Popular Resistance fighters fighting on the side of President Abd-Rabbu Mansour Hadi’s forces expelled the Houthis and their allies from the southern port city of Aden, whose capture by the rebels sparked the aerial campaign by the Arab coalition.
More than 4,300 people have been killed in the conflict in Yemen, according to the UN, almost half of those civilians.
At least 50 people have died in Houthi attacks on positions inside Saudi Arabia.