President Viktor Yushchenko summoned several thousand interior troops to the Ukrainian capital Saturday but forces loyal to the nation's prime minister stopped them outside Kiev, raising fears that the two leaders' months-long struggle could turn violent. Tensions between Yushchenko, who has sought to lead Ukraine into the European Union and NATO, and his rival, Prime Minister Viktor Yanukovych, who seeks to preserve Ukraine's close ties with Moscow, have been building since the president ordered parliament disbanded in April and called new elections. But the political struggle threatened to turn into a physical confrontation this week when Yushchenko ordered the dismissal of the nation's chief prosecutor, loyal to the prime minister, who refused to leave his office. Riot police surrounded the prosecutor's offices, preventing his eviction. Yushchenko issued a decree Friday that put the nation's 32,000 Interior Ministry troops under his command, and has ordered some of them to the capital.