KIEV (REUTERS) - Fighting broke out among members of Ukraine's ruling coalition in parliament on Friday after a member of President Petro Poroshenko's bloc physically picked up Prime Minister Arseny Yatseniuk and pulled him from the podium.

Mr Yatseniuk was defending his embattled government's record when lawmaker Oleh Barna walked over to him, presenting him sarcastically with a bunch of red roses.

Mr Barna then grabbed him around the waist and groin, lifting him off his feet and dragging him from the rostrum.

Members from Mr Yatseniuk's People Front party waded in, pushing Mr Barna and throwing punches. Lawmakers from Mr Poroshenko's bloc joined the fray and an angry brawl ensued for several minutes before deputies returned to their seats.

The incident exposed deep divisions in the pro-Europe coalition that have fuelled speculation the government could fall even as Ukraine's Western backers warn that time is running out for Kiev to make good on its promises to root out endemic corruption and cronyism.

Mr Yatseniuk is, like Mr Poroshenko, a pivotal player in the pro-Western leadership that emerged after the downfall of the Moscow-backed Viktor Yanukovich in February 2014. But support for him has fallen dramatically in the past year.

"The atmosphere in the room provoked mentally unbalanced people. Oleh Barna served on the frontline and is therefore too impulsive, but that does not excuse his actions," the head of Mr Poroshenko's bloc Yuriy Lutsenko told journalists.

The brawl interrupted a question-and-answer session with Mr Yatseniuk, 41, after he delivered a summary of the performance of his government, which after exactly one year in power is now no longer immune from being dismissed by parliament.

"I told you a year ago that nobody is going to promise the moon," Mr Yatseniuk said, appearing to defend his cabinet from accusations they have not made good on their reform promises.

"You have full constitutional right to vote on the question of dismissing Ukraine's cabinet. Put it to the vote. I'll accept the decision of the Ukrainian parliament. I'm not clinging to this chair," he said.

Opposition parties are calling for a no-confidence motion to be tabled and commentators say enough votes could be gathered to dismiss the government, but a vote is not yet likely due to the lack of a candidate to replace Yatseniuk.

In an impassioned speech on Tuesday, US Vice-President Joe Biden urged parliament to put their differences aside to approve reforms, including critical tax and budget bills and judicial changes, without which he said Ukraine would fail to rebuild itself on transparent, democratic lines.

"The President, the Prime Minister, the members of this august body - all of you must put aside parochial differences ...If you fail, the experiment fails," he told parliament.

A disagreement over proposed tax amendments and the draft 2016 budget has delayed the disbursement of up to US$4 billion in international loans which Ukraine had hoped to secure to boost its war-torn finances before the end of the year.

Mr Yatseniuk said the government had submitted a "compromise"tax reform bill and urged lawmakers to approve the amendments before the turn of the year.

Mr Yatseniuk's People's Front party triumphed in parliamentary elections in 2014, but the approval rating for the party is now around 1 per cent.