* Activists occupy justice ministry building overnight
* Yanukovich, opposition prepare for parliament session
* EU voice concern over disappearances, reported torture
By Richard Balmforth
KIEV, Jan 27 (Reuters) - Ukraine's justice minister threatened on Monday to press for a state of emergency if protesters did not vacate a ministry building they occupied overnight in the third such action in street protests against President Viktor Yanukovich's rule.
A State of Emergency would limit movements of people and vehicles, ban rallies, marches and strikes, suspend the activity of political parties and introduce a curfew.
The main 'frontline', where radical activists face police lines in front of Dynamo football stadium, remained calm. But about 50 masked men stormed into the justice ministry building in downtown Kiev and refused police orders to leave.
Raising tension ahead of an emergency session of parliament on Tuesday called to defuse the crisis in which six people have been killed, Justice Minister Olena Lukash said:
"If the justice ministry building is not vacated immediately, I will be forced to appeal ... to the Council for National Security and Defence with a demand that introduction of a state of emergency in the country be discussed."
The occupation of the ministry building was the third such action in four days.
Protesters occupied the agricultural ministry on Friday and only agreed to leave the energy ministry which they entered on Saturday after the minister warned their action could disrupt energy supplies in the country.
Yanukovich triggered the unrest in November when he abruptly abandoned plans to sign association and free trade deals with the European Union, opting instead to tighten economic ties with former Soviet master Russia, and angering millions who dream of a European future.
Apart from clashes between radicals and police, several hundred people camp now round the clock on Kiev's Independence Square and along an adjoining thoroughfare,
The unrest has spilled over into other regions of the country of 46 million people, including areas of eastern Ukraine and the south which are traditionally pro-Yanukovich areas.
Ukraine on Monday announced it would draw on another $2 billion of credit - adding to $3 billion already received for purchase of a bond - from a $15 billion bailout package offered by Moscow after the former Soviet republic walked away from the deal with the EU.
But though the Russian aid package will help Ukraine handle $8 billion of foreign debt this year and boost depleted reserves, this does not seem to be impressing thousands on the streets who are pressing for hard political concessions from Yanukovich.
GOVERNMENT POSTS OFFERED
Yanukovich on Saturday offered top government posts to opposition leaders - the prime minister's job to former economy minister Arseny Yatsenyuk and a deputy prime minister's portfolio to boxer-turned-politician Vitaly Klitschko - in his first concessions in two months of unrest.
But the opposition sees this is an attempt to divide them and are pressing for more concessions, including early elections, setting the stage for a tough political battle when parliament meets on Tuesday.
The opposition is also seeking the repeal of anti-protest legislation rushed through parliament on Jan 16 by Yanukovich loyalists which triggered a violent outburst among radical activists three days later.
Western governments have backed the opposition in denouncing the legislation, which places curbs on media as well as banning virtually all forms of protest, as anti-democratic.
In a statement on Monday, EU national envoys called on all sides "to revoke the whole package of legislative acts restricting the exercise of fundamental freedoms" and urged the government to keep its promises to the opposition.
Western governments are also expressing increased concern over the security situation in Ukraine against a background of reports of abductions, including by police, as well as the violent clashes between radical activists and police.
"We express concern abou the deteriorating human rights situation. Arrests of wounded people in front of clinics, several cases of disappearance and reported torture are extremely worrying and can be accepted under no circumstances," the EU statement said.
EU foreign policy chief Catherine Ashton is due to visit Kiev on Thursday and Friday.
The United States has warned Yanukovich that failure to ease the standoff could have "consequences" for its relationship with Ukraine. Germany, France and other Western governments have also urged him to talk to the opposition.
Russia has stepped up its warnings against international interference in Ukraine, telling European Union officials to prevent outside meddling and cautioning the United States against inflammatory statements. President Vladimir Putin is due to visit Brussels on Tuesday for what promises to be a tense EU-Russia summit.
Despite Lukash's warning, most analysts believe that declaring a state of emergency is not something envisaged by the Yanukovich leadership now since it would have a drastic effect on Ukraine's relations with the West and squeeze foreign investment further.
Defence Minister Pavlo Lebedev repeated at the weekend that, according to the constitution, the army can not be used in settling internal conflicts in the country.
(Additional reporting by Natalia Zinets and Pavel Polityuk; Writing By Richard Balmforth)