By Maria Golovnina ISLAMABAD (Reuters) - Pakistan slipped deeper into crisis on Thursday after talks between the government and the opposition failed and protesters prepared for what their leaders declared would be a "deciding day" in their bid to bring down the prime minister. Pakistan has been gripped by mass protests for two weeks, with thousands of demonstrators led by cricketer-turned-politician Imran Khan and firebrand cleric Tahir ul-Qadri camped outside parliament in a country prone to military coups. In a bid to resolve the standoff, government representatives have held sporadic talks with protest leaders, but the latest round of negotiations ended inconclusively.