Sanaa, Yemen (CNN)A border guard was killed in a cross-boundary fire exchange with militants in Yemen this week, the state-run Saudi Press Agency reported Thursday — marking Saudi Arabia’s first publicly known military death since it launched airstrikes against rebels inside its southern neighbor.

The clash occurred Wednesday night at the border in southwestern Saudi Arabia’s Asir region, when militants in a mountainous area on the Yemeni side fired on Saudi border troops, prompting them to return fire, SPA reported.

Besides the slain border guard — identified as Cpl. Salman Ali Yahya al-Maliki — 10 others suffered injuries that were not life-threatening, the Saudi media outlet said.

On Thursday, Houthi rebels seized the presidential palace in the southern Yemeni port city of Aden, a neutral security official and two Houthi commanders in Aden told CNN.

The palace had been where President Abdu Rabu Mansour Hadi, who fled the country last month, had stayed for a period of time after Houthis secured control of the capital, Sanaa, in January.

According to the security official, Houthis now control most large districts in Aden amid ongoing clashes.

Yemeni special forces, considered pro-Houthi and loyal to former President Ali Abdullah Saleh, arrived in Aden on Thursday in an attempt “to secure the city,” a Saudi official with knowledge of the situation told CNN.

“I can now confirm that it is not Saudi special forces who have landed but Yemeni special forces loyal to Saleh who landed by small boat. They are few in number and have made their way to the old parliament building,” the intelligence official said.