(WARSAW) - Poland's pro-EU Prime Minister Donald Tusk announced Wednesday talks with eurosceptic President Lech Kaczynki, in an effort to solve a bitter spat over the EU's Lisbon Treaty.

Tusk told reporters he was due to meet with Kaczynski on Thursday.

"The signals coming from the presidential palace and the (opposition) suggest there has been a positive development, to the point that I am hopeful, provided this development continues," he said.

The president's twin brother Jaroslaw Kaczynski, head of the opposition conservative-nationalist Law and Justice party, has been threatening for weeks to block the treaty's ratification in parliament.

Tusk needs the votes of Law and Justice because his own liberal Civic Platform and its allies lack the required two-thirds majority to approve the reform treaty, which must be ratified by all 27 EU member states in order to come into force.

Last week, Lech Kaczynski said he was confident Poland would ratify the treaty by the end of April.

The twins are pushing a draft ratification law submitted by the president, which Lech Kaczynski has said is designed to protect Poland's national interests better than Tusk's variant.

Tusk's party has proposed a simple green light ratification package for the treaty, which is designed to streamline decision-making in the EU.

The Kaczynskis' stance has caused a major spat in Poland, with the brothers facing accusations of hypocrisy, given that they helped negotiate the treaty last year and at the time trumpeted it as a success for Poland.

Jaroslaw Kaczynski lost power to Tusk in snap elections last October. Lech Kaczynski, who pipped Tusk in the 2005 presidential election, still has almost three years left in office.

Lech Kaczynski has insisted his ratification proposal would guarantee Poland's ability to invoke the so-called "British protocol" opt-out of the Lisbon Treaty's Charter of Fundamental Rights and thus avoid European Court of Justice rulings on an array of issues.

He has argued the charter could otherwise let Germans sue Poles for properties lost after border changes following World War II, and allow homosexual marriage in Poland, a devoutly Catholic country.

Tusk has warned he could call a referendum on the treaty, should it fail to clear parliament. A solid 65 percent of Poles would vote yes, 15 percent no and 20 percent remain undecided, according to a recent survey.

Adopted by EU leaders in December, the treaty replaces the bloc's defunct draft constitution, torpedoed by French and Dutch voters in referendums in 2005.

The aim is to have the Lisbon Treaty in force by next year, provided all 27 member states have ratified it.

Lawmakers in Bulgaria, France, Hungary, Malta, Romania and Slovenia have already approved the accord.

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