Ukraine is defying demands to let Yemen join the World Trade Organization and has accused other countries of violating its sovereignty and their own responsibility to remain neutral.

Kiev - Ukraine's two leading opposition parties joined forces on Monday ahead of an October parliamentary election, forging an alliance they hope will defeat President Viktor Yanukovich's Party of the Regions which has a majority in the single-chamber legislature.

Batkivshchyna (Fatherland), the party of jailed former prime minister Yulia Tymoshenko, and Front of Changes, led by technocrat Arseniy Yatsenyuk, said their alliance, which is temporary rather than a fully-fledged merger, was strategic.

“Our political forces will come up with a single (candidate) list for the elections and agree on single-seat constituency candidates,” the parties said in statements.

“(The list) will be led by Yulia Tymoshenko and Arseny Yatsenyuk as the most popular opposition politicians.”

Polls show the two parties could beat the Party of the Regions in the part of the election where seats are allocated according to party lists and a system of proportional representation.

Half the chamber's 450 seats are distributed in this way.

However, analysts say the two parties will face an uphill battle in single-seat constituencies where the winner is decided by a simple majority. The other 225 seats are decided in this way.

Tymoshenko, 51, Yanukovich's arch rival, was sentenced to seven years in prison last October after being found guilty of abusing her power when she was prime minister. She is now being tried - in absentia at her own request - on charges of tax evasion, meaning it is highly unlikely she would be able to take up a seat in parliament.

Having her name on the ballot could help the opposition secure more support, however.

Yatsenyuk, 37, has served as a deputy central bank governor, economy minister, foreign minister and as speaker of parliament.

According to a March survey by pollster Research and Branding Group, 15 percent of Ukrainians support Batkivshchyna, while 9 percent side with the Front of Changes. The party of the Regions was backed by 18 percent of respondents.

“Today, the opposition can count on (winning) 170 seats in the new parliament, including 40-45 mandates in single-seat constituencies,” said political analyst Volodymyr Fesenko.

In the current parliament, Tymoshenko's faction has 100 seats, while the Party of the Regions has 191. The rest are split between smaller factions aligned with either of the two and non-aligned deputies.

Tymoshenko became famous as a leader of the 2004 Orange Revolution which derailed Yanukovich's first bid for the presidency. She has since served twice as prime minister but lost the 2010 presdential vote to Yanukovich in a close race.

After losing power, Tymoshenko and a number of her allies faced corruption-related charges in what she described as a crackdown on the opposition. The European Union said their trials were examples of “selective justice”. - Reuters