ANKARA - Police sealed off a hotel in Ankara on Sunday, preventing dissidents in Turkey's nationalist opposition from holding a party congress that could jeopardize President Tayyip Erdogan's plans for more power.Several hundred members of the Nationalist Movement Party (MHP) have launched a bid to oust Devlet Bahceli, leader for much of the last two decades. To do so they need to change party rules at a special congress.The AK Party needs the MHP's support to change the constitution to give Erdogan more powers. Bahceli loyalists seem willing to do this, but dissident leaders, including former interior minister Meral Aksener, have said they will oppose the plan.Dissident leaders issued a statement on Sunday accusing Erdogan's AK Party of intervening to try to block the congress."The executive branch staged a coup against the judiciary branch. The constitution and law are being suspended. A change in the MHP became the AK Party government's nightmare," the dissidents said in their statement.