GUATEMALA CITY (Reuters) - Guatemalan police raided the headquarters of presidential candidate Bernardo Arevalo's Semilla party, the attorney general's office announced on Friday, just a month before the high-stakes run-off election.

       The raid follows an investigation into alleged irregularities in the party's membership list, which has been widely criticized by rights groups as improper interference in Central America's biggest democracy.

       A court ordered the suspension of the party earlier this month shortly after the June 25 first-round presidential vote, in which the center-left Arevalo running on an anti-corruption platform shocked the country by securing second place and advancing to the August 20 run-off.

       The targeting of Arevalo's party, which centers on alleged irregularities in the registration of more than 5,000 Semilla members, has injected fresh turmoil into the race to succeed outgoing conservative President Alejandro Giammattei.

       Guatemala's top court granted the party an injunction and ruled that there are no legal impediments to Arevalo competing in the run-off election in which he is running against former First Lady Sandra Torres, who finished first in June.

       Guatemalan authorities also raided the electoral tribunal's building earlier this month, also linked to the Semilla party's membership registration.

       (Reporting by Sofia Menuchu; Writing by Valentine Hilaire; Editing by David Alire Garcia)

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