MADRID (Reuters) - Spain's acting Prime Minister Mariano Rajoy on Thursday said he had accepted a mandate from the King to form a government although he did not yet have enough backing to seek the confidence of the parliament.

Rajoy left the date open for such a parliamentary vote to happen and said he would open a round of talks with other parties to try and convince them to vote for his conservative People's Party.

Most parties said this week said they would not vote in favor of the PP, which has 137 seats in the parliament when 176 are needed to reach a majority.

"We need to form a solid and stable government as soon as possible," Rajoy told a news conference after meeting with King Felipe.

"Spain needs a government now, this government should be headed by the PP and there is no alternative to this," he also said.

(Reporting by Julien Toyer; Editing by Sonya Dowsett)