Journalists at the only television channel in Ukraine to give the opposition air time ahead of a tight presidential election staged a hunger strike yesterday to denounce official pressure in the ex-Soviet state.

With five days to go in a campaign pitting the country's prime minister against a liberal challenger, Russian President Vladimir Putin was scheduled to make an unprecedented television appearance, answering questions from Ukrainian viewers.

With Russian influence still considerable 13 years after independence from Moscow, Mr Putin has given every indication he backs Prime Minister Viktor Yanukovich against opposition hopeful Viktor Yushchenko. The two contenders are in a virtual dead heat in polls and a run-off next month is almost certain.

Outgoing president Leonid Kuchma, who cancelled a trip to Poland in view of mounting pre-election tensions, issued a new assurance that the poll would be free of cheating.

Mr Yanukovich is backed by Mr Kuchma, who is stepping down after a decade in power marked by impressive economic growth but also far-reaching political scandals.

Channel 5 the only channel covering Mr Yushchenko's campaign, proceeded with broadcasts while showing staff clad in white headbands and t-shirts drinking water out of plastic cups.

"This is political blackmail. We have been told that at election time we should all shut up," Andriy Shevchenko, the channel's chief editor, said.

Some 7,000 students massed in support of the protest in the western city of Lviv, a Yushchenko stronghold.

Reporters say procedures to prevent the channel broadcasting nationwide, a court case which has frozen its bank accounts and threats to curtail its licence are politically driven.

Most television channels and major newspapers are controlled by the government or powerful businessmen close to Mr Kuchma.

Washington and the EU have urged Ukraine to stage free elections. Both cite media restrictions as a main concern in a campaign punctuated by charges of dirty tricks and suggestions by each side that the other may disrupt the vote.

Passions have boiled over into minor clashes, including altercations after Mr Yushchenko drew 100,000 supporters to a weekend rally in Kiev.

Mr Kuchma renewed his promise that the election, the fourth since Ukraine declared independence, would reflect the will of Ukraine's 47 million people.