Rights groups say police are intensifying threats against activists ahead of national voting

Rights groups say police in Zimbabwe have increased threats against civic groups a week away from a referendum on a new constitution and crucial elections to end the nation's shaky coalition later this year.

An alliance of 15 human rights, pro-democracy and labor groups said Saturday police mounted "a sustained and escalating assault" on activists to discredit their organizations ahead of polling. The state Electoral Commission announced Friday that groups under police investigation or leaders facing any charges will not be allowed to observe the referendum vote next Saturday.

At least three main groups, including the independent Zimbabwe Election Support Network, are so far affected after police raids on their offices this year.

The alliance said most civic groups are facing "vague and generalized search warrants, arrests, persecution and prosecution."