UN Secretary-General Ban Ki-moon on Monday condemned the assassination in Yemen's capital Sana'a last week of Iranian cultural attache Abolqassem Assadi, his deputy spokesman Farhan Haq told the daily press briefing.Expressing his condolences to Assadi's family and the Iranian Government, Ban called for the perpetrators of this "crime" to be brought to justice.Haq said Ban is concerned that terrorist attacks and hostage-taking have continued in Yemen, and calls for the immediate release of all hostages in Yemen.He recalled that according to the 1979 International Convention, hostage-taking is an offence of grave concern to the international community.