Ukraine's prime minister accused President Viktor Yushchenko of preparing to use force in their struggle for supremacy after Yushchenko said he was taking control of interior ministry troops.
Yushchenko issued his decree hours after riot police loyal to the prime minister took over a building housing the prosecutor general's office in Kiev following scuffles.
The decree concerns troops largely responsible for maintaining public order and not the army, which is controlled by one of pro-western Yushchenko's few allies in the cabinet.
He ordered the interior ministry troops to protect key sites.
Yanukovich denounced the president's move as dangerous and unconstitutional.
It presaged, he said, an attempt to use force to resolve Ukraine's long-running political crisis.
"Taking such decisions without consulting the government is inadmissible. I think this seriously aggravates the situation," Yanukovich told a cabinet meeting.
"What does all this mean? This means that the 'use of force scenario', which we have been discussing constantly, has begun."
It was reported today that several thousand interior ministry troops are moving towards the capital, Kiev.
Yushchenko and Yanukovich, who is friendlier to Moscow, have been sniping for months over a division of powers.
They have failed to agree a date for a snap parliamentary election nearly two months after the president dissolved the chamber.
Tensions boiled over on Thursday when Yushchenko dismissed the prosecutor general and accused riot police who rushed to his office to defend him of breaking the law.