MADRID (AP) — Spain's ruling conservatives will win the most seats in Dec. 20 general election but will need substantial outside support to stay in office, according to a government-run opinion poll released Thursday.

The much-watched CIS survey — the last one before the vote — said Prime Minister Mariano Rajoy's Popular Party would garner 28.6 percent of vote, or up to 128 seats in the 350-deputy Parliament, way below the 176 seats needed for a majority. The opposition Socialist party would bag 20.8 percent of the vote for a possible 89 seats.

The centrist newcomer Citizens party could garner 66 seats while the radical leftist We Can party may obtain 25 seats.

The CIS said the poll had a margin of error of 0.76 percentage points. It said 17,452 people were quizzed in person from Oct. 27-Nov. 16.

The result contrasts with many recent newspaper-commissioned polls that show the top three parties more evenly matched. Campaigning begins at midnight Thursday.

In 2011, the Popular Party won a record majority of 186 seats as it captured 45 percent of the vote.

But its popularity has waned chiefly because of its inability to fulfill a 2011 promise to greatly reduce unemployment, which at 21 percent is just two percentage points less than when it took office. The party has also been implicated in myriad corruption cases.

In a pre-campaign comment on his official Twitter account, Rajoy boasted that the government had recovered 1 million jobs destroyed in the crisis.

"Among the major European economies, we are the one growing most," Rajoy said.