WASHINGTON, Feb. 17 (Xinhua) -- The United States on Monday condemned a bombing attack on a tourist bus in Egypt Sunday, in which three nationals of the Republic of Korea (ROK) and one Egyptian driver were killed.

　　"We condemn this cowardly attack on innocent tourists," said State Department spokeswoman Jennifer Psaki in a statement, voicing her "deepest condolences" to the families of the ROK victims.

　　An explosion ripped through the front part of the tourist bus, with 33 ROK nationals aboard, when it waited in line near the Taba border crossing between Egypt and Israel in Sinai Peninsula, killing four and injuring 13 others.

　　Since the military's removal of Mohamed Morsi, Egypt's first elected president, in July 2013, Sinai has witnessed a deteriorating security situation, with some radical militants taking neighboring Israel as a stronghold for launching attacks on checkpoints and police stations in Sinai, causing heavy casualties.

　　No claim of responsibility has been made for the bombing.