KYIV, Ukraine — Ukrainian President Viktor Yushchenko said Friday he was taking command of Ukraine's Interior Ministry troops, but a ministry spokesman rejected the order in a move of defiance that dramatically escalated the country's political turmoil.

Tensions between Yushchenko and his rival, Prime Minister Viktor Yanukovych, have been building for weeks, and the president's order, reflecting doubt on the loyalty of servicemen under the ministry's command, appeared to suggest rising concern over possible clashes.

On Thursday, the Interior Ministry, led by an ally of Yanukovych, sent police to surround the office of the prosecutor-general, whom Yushchenko had just fired.

A statement on the presidential Web site said Yushchenko's order for the troops to be under his command was necessary "to prevent using Interior Ministry troops in the interest of some political forces that cause a threat for Ukraine's national security."

In rejecting Yushchenko's order, Interior Ministry spokesman Konstantin Stogniy said it was illegal, and "fulfilling illegal orders is a crime."

Despite the rejection, the Interfax news agency quoted Yushchenko aide Viktor Bondar as saying that the command had confirmed its readiness to follow Yushchenko's order. The troops are led by Gen. Oleksandr Kihtenko, who is seen as a Yushchenko ally.

The Interior Ministry has about 32,000 troops and 220,000 regular police under its control; Yushchenko's order calls for his taking control only of the troops.

Thursday's dismissal of Prosecutor-General Svyatoslav Piskun, a Yanukovych ally, severely aggravated tensions that have been running high since Yushchenko's April 2 order dissolving parliament and calling early elections.

The president said was the moves were necessary because Yanukovych and his coalition were trying to usurp presidential power. The parliament, where Yanukovych leads the majority coalition, has defied the order, calling it unconstitutional.

The dissolution order has led to weeks of argument and competing demonstrations between backers of the president and of the premier, but no disorder has broken out.

Piskun last year was elected to the national parliament as a member of Yanukovych's party. Yushchenko said it was illegal for Piskun to be both a member of parliament and prosecutor-general, but the matter was complicated by the dispute over whether the parliament still legally exists, as Yushchenko had ordered it dissolved last month.

Both Yushchenko and Yanukovych had agreed to respect the Constitutional Court's decision on the dissolution order. But the court has been deliberating on the matter for weeks, and the deliberations were complicated by Yushchenko's orders to fire several of its judges, including the chief judge.

Yushchenko came to office in 2005 after the bitter Orange Revolution -- massive protests that broke out after Yanukovych was counted as winner of a fraud-plagued presidential ballot. The Supreme Court annulled that vote and Yushchenko won a rerun.

But Yushchenko's goal of instituting political and economic reforms in the ex-Soviet nation have run aground over factional fighting among his supporters. In last year's parliament elections, Yanukovych's party won the largest share of seats, apparently benefiting from wide voter dissatisfaction with the country's stalled reforms and internecine political sparring.

Yushchenko has repeatedly declared his aim to bring Ukraine closer to the West, including eventual membership in NATO and the European Union. But the chronic political turmoil of his presidency has frustrated those aims and raised increasing criticism of him for actions that are either ineffectual or unilateral.