Poland's ruling party leader has pledged more social benefits for families with children as he opened the party's campaign ahead of key elections this year.

Speaking at a party convention Saturday, Jaroslaw Kaczynski announced upgrading the generous social program of his right-wing Law and Justice party, which is enjoying the highest social backing ever since it won power in 2015.

But opinion polls show the party could lose to a united opposition in European Parliament elections in May and to the national parliament in the fall.

Poland's most powerful politician, Kaczynski is also facing allegations of soliciting a bribe and unlawful participation in business negotiations.

He promised expanding family benefits to cover every child, abolishing tax for young employees and more payouts for retired people.