(Adds details on referendum-related sanctions, Baltic gas pipeline leaks, Zelenskiy address)
Ukraine, West say Russian vote was a farce
Tribune erected on Red Square proclaiming provinces are Russia
Zelenskiy attempts to rally international support
U.S. to keep rolling out sanctions on Moscow
By Jonathan Landay
ZAPORIZHZHIA, Ukraine, Sept 28 (Reuters) - Moscow was poised on Wednesday to annex a swath of Ukraine, releasing what it called vote tallies showing support in four partially occupied provinces to join Russia, after what Kyiv and the West denounced as illegal sham referendums held at gunpoint.
On Moscow's Red Square, a tribune with giant video screens has been set up, with billboards proclaiming "Donetsk, Luhansk, Zaporizhzhia, Kherson - Russia!"
President Vladimir Putin could proclaim the annexation in a speech within days, just over a week since he endorsed the referendums, ordered a military mobilisation at home and threatened to defend Russia with nuclear weapons if necessary.
The Russian-installed administrations of the four Ukrainian provinces on Wednesday formally asked Putin to incorporate them into Russia, which Russian officials have suggested is a formality.
"The results are clear. Welcome home, to Russia!," Dmitry Medvedev, a former president who serves as deputy chairman of Russia's Security Council, said on Telegram.
Russian-backed authorities claim to have carried out the referendums over five days in parts of eastern and southern Ukraine that makes up around 15% of the country's territory.
Residents who escaped to Ukrainian-held areas in recent days have told of people being forced to mark ballots in the street by roving officials at gunpoint. Footage filmed during the exercise showed Russian-installed officials taking ballot boxes from house to house with armed men in tow.
"They can announce anything they want. Nobody voted in the referendum except a few people who switched sides. They went from house to house but nobody came out," said Lyubomir Boyko, 43, from Golo Pristan, a village in Russian-occupied Kherson province.
Russia says voting was voluntary, in line with international law, and that turnout was high. The referendums and notion of annexations has been rejected globally, as was Russia's 2014 takeover of Crimea from Ukraine.
Ukrainian President Volodymyr Zelenskiy sought to rally international support against possible Russian annexations in a series of calls with foreign leaders, including those of Britain, Canada, Germany and Turkey.
"Thank you all for your clear and unequivocal support. Thank you all for understanding our position," Zelenskiy said in a late-night video address.
The United States said it would in coming days impose economic costs on Moscow for the referendums, adding to several tranches of sanctions since Russia's invasion of Ukraine in February that has destroyed cities and killed thousands.
"We will continue to work with allies and partners to bring even more pressure on Russia and the individuals and entities that are helping support its attempted land grab," State Department spokesperson Ned Price told reporters.
The European Union's executive also proposed more sanctions against Russia, but the bloc's 27 member countries will need to overcome their own differences to implement them.
Denis Pushilin, the Russian-installed leader in Donetsk province, said he was on his way to Moscow to complete the legal process of joining Russia.
"Now we are moving to a new stage of military action," he said, amid speculation that Putin is set to change the status of what he has so far called a "special military operation" to a counter-terrorism operation.
Russian officials have said any attack on annexed territory would be an attack on Russia itself.
Putin altered his strategy following a stunning setback for Russian forces in the northeastern region of Kharkiv earlier in September, when Ukrainian troops recaptured dozens of towns and villages. He also announced the swift call-up of hundreds of thousands of Russian men to fight, and issued a new warning about the possible use of nuclear weapons.
Kremlin spokesman Dmitry Peskov said Russia would need to keep fighting until it had taken control of all of Donetsk. Around 40% is still under Ukrainian control and the scene of some of the war's heaviest fighting.
The general staff of the Ukrainian armed forces said 11 Russian attacks had been repelled on Wednesday, most of them north of Donetsk. Russian forces had shelled dozens of towns along the length of the front line, it said in a Facebook post.
Reuters was not able to verify battlefield reports.
GAS PIPELINE 'SABOTAGE'
The Russian annexation plan gathered pace as leaking gas bubbled up in the Baltic Sea for a third day after suspected explosions tore through undersea pipelines built by Russia and European partners. The Nord Stream 1 pipeline, once the main route for Russian gas to Germany, was already shut but cannot now be easily reopened.
NATO and the European Union warned of the need to protect critical infrastructure from what they called "sabotage", though officials stopped short of assigning blame. Russia's FSB security service is investigating the damage sustained to the pipelines as "international terrorism", the Interfax news agency cited the general prosecutor's office as saying.
The Nord Stream pipelines have been flashpoints in an expanding energy war between Moscow and capitals in Europe that has damaged major Western economies and sent gas prices soaring.
The United States believes it is too soon to conclude there was sabotage, a senior U.S. military official told reporters in Washington on Wednesday. "The jury is still out," the official said.
Meanwhile, the United States unveiled a $1.1 billion weapons package for Ukraine that includes 18 High Mobility Artillery Rocket System (HIMARS) launchers, accompanying munitions, various types of counter drone systems and radar systems. The announcement brings the U.S. security aid to $16.2 billion.
(Reporting by Reuters bureaux Writing by Andrew Osborn, Toby Chopra and Grant McCool; Editing by Peter Graff, Hugh Lawson and Bill Berkrot)