Before the mass rally, the largest since "Orange Revolution" protests engulfed Ukraine in 2004, Yushchenko issued a new threat to dissolve parliament and call just such an election.
His arch rival, Prime Minister Viktor Yanukovich, back in power after being humiliated in that upheaval, told a rally of his own supporters he would ignore the president's "ultimatums".
Yushchenko, his powers cut by constitutional change, has sniped for months with his rival. Former prime minister Yulia Tymoshenko has led an opposition drive for a new election to bolster the president's policy of moving closer to the West.
"It is not just the president's right to dissolve parliament," Tymoshenko told a cheering crowd in Independence Square, where she rallied supporters in the 2004 protests.
"It is his duty to dismiss this corrupt, treacherous assembly and go ahead with an open, honest early election in which there can be no doubt democratic forces will win."
Sporting her trademark peasant braid, she told supporters the liberal leaders of the 2004 revolution had been naive to believe they would achieve their aims painlessly.
"Above all else, we need an early election to show our people again that we are capable," she told the crowd.
Tymoshenko was the president's first prime minister after he swept to victory in the re-run of a rigged election. But she was fired within eight months after her government split into two camps, each accusing the other of corruption.
Yushchenko reluctantly appointed Yanukovich prime minister last year after his own allies scored badly in a parliamentary election and failed to form a government.
PRESIDENT ACCUSES PRIME MINISTER
The president accused the prime minister this week of illegally trying to expand the parliamentary coalition supporting him. He told supporters he could dissolve the chamber and hold a new poll.
"If the actions of the majority in parliament do not return to a constitutional basis, I will sign a decree dissolving parliament," he told a congress of his Our Ukraine party.
He issued a series of demands to parliament, including a call to approve a law barring deputies from switching parties.
Yanukovich, friendlier to Moscow, says the president has no grounds to dissolve parliament. He told supporters massed scant metres from the opposition he would tolerate no such demands.
"We will never accept ultimatums that are outside the realm of law and the constitution," he told a 10,000-strong crowd.
Yanukovich agreed last year to leave intact the president's policies of seeking European Union and NATO membership. But his government has since chipped away at Yushchenko's authority.
Yanukovich can count on about 250 votes in the 450-seat assembly and has vowed to expand his coalition to 300, a figure that could allow him to engineer further constitutional change.
The president has summoned party leaders for talks on Monday as required by the ex-Soviet state's constitution for any decision to dissolve parliament and proceed with an election.
A poll published this week put Yanukovich's Regions Party in the lead with 18 percent support. Tymoshenko's bloc was second with 15 percent and Our Ukraine lay third with 7 percent.
Source: Scotsman News