Police tightened security in Thailand's capital on Saturday as thousands of protesters rallied outside a state telecommunications group and vowed to occupy prime minister Yingluck Shinawatra's office to paralyse her administration. Faced with dwindling support, demonstrators have started to up the ante. They burst into the headquarters of the army on Friday, urging it to join their side in a complex power struggle centred on the enduring political influence of Ms Yingluck's billionaire brother, ousted prime minister Thaksin Shinawatra.