The International Committee of the Red Cross (ICRC) said that two of its staff members were killed in Yemen on Wednesday.
The two were shot and killed while they were travelling with colleagues in a convoy between Saada and Sana'a cities, it said in a press release.
It is believed a single gunman opened fire on the convoy killing one of them immediately and the second later died at hospital, the statement said, pointing out they were Yemeni citizens and had worked as a field officer and as a driver.
"The ICRC condemns in the strongest possible terms what appears to have been the deliberate targeting of our staff," said the head of the ICRC delegation in Yemen, Antoine Grand.
"It is premature for us at this point to determine the impact of this appalling incident on our operations in Yemen. At this time, we want to collect ourselves as a team and support each other in processing this incomprehensible act," said Mr Grand.
It is not yet clear who carried out the attack, it added.
Aid agencies including ICRC are facing big challenges including attacks on their staffs and offices amid the six-months armed conflict in the country.
Lately, gunmen stormed ICRC offices in some cities, threatened staffs with guns and looted equipment forcing the Aden office to suspend its activities.
Public facilities including hospitals have been also attacked as international organizations are accusing all the warring parties of violating the law of war.
The armed conflict including a blockade on all sea, land and air ports has left Yemen to face lacks and shortages of all supplies primarily food and medicines.
The blockade was part of the Saudi-led military intervention launched in March against the Houthi militants who ousted the government in late 2014.