Bulgaria's interior minister says up to five people assisted a bomber who killed five Israeli tourists and a Bulgarian bus driver in July.

In an interview for the 24 Chassa daily Thursday, Tsvetan Tsvetanov said "between three and five foreigners" were involved in the bombing plotted "outside Bulgaria over a period of a year and a half." No arrests have been made. The bomber also died.

According to Tsvetanov, "lots of evidence" has been collected but added that the "time has not yet come to voice any concrete accusation against the people or groups who performed this terrorist act." He says "we have to be very cautious as national security is concerned."

Bulgarian officials have declined to back up Israel's claims that Iran and the militant group Hezbollah played roles.