Britain's chief prosecutor has blocked an attempt to serve visiting Israeli politician Tzipi Livni with an arrest warrant for war crimes, stemming from her time as Israel's foreign minister.

The decision by Director of Public Prosecutions Keir Starmer Thursday comes weeks after Britain revised its law on universal jurisdiction.

The revised law allows British courts to prosecute foreigners accused of crimes against humanity, wherever they were committed. But such prosecutions require the consent of the director of public prosecutions.

Before the law was revised, private individuals could start criminal prosecutions in such cases by applying to a magistrate.

Starmer would not identify who requested Livni's arrest. But the matter reportedly involves Israel's 2008 offensive in Gaza. Livni was foreign minister at the time.

Before it was revised, the law strained British-Israeli relations, as some Israeli officials cancelled trips rather than face arrest.