Berlin, Sep 23 (IANS): German Chancellor Angela Merkel Monday said she has already contacted the Social Democrats' (SPD) leadership on possible coalition negotiations but did not rule out talks with other potential coalition partners.

"We are, of course, open for talks and I have already had initial contact with SPD chairman, who said the SPD must first hold a meeting of its leaders Friday," Xinhua quoted Merkel as saying in a news conference, adding that she did not exclude talks with other potential partners.

Merkel's Christian Democrats Union (CDU) along sister Bavarian party the Christian Social Union (CSU) proved to be the biggest winner with 41.5 percent of votes in the federal election, the official provisional result showed.

It showed the largest opposition party, the centre-left SPD took 25.7 percent of votes.

The Green party, the SPD's favoured ally, captured 8.4 percent. The Left Party got 8.6 percent of votes.

Without a majority of the parliament seats, the CDU-CSU union has to find a partner to form a coalition in order to rule Europe's largest economy for the next four years.

Up to weeks of horse trading is expected for forming a grand coalition.

A grand coalition with the centre-left SPD as in Merkel's 2005-2009 first term seems probable.

Merkel's current junior coalition partner, the pro-business Free Democratic Party (FDP) failed to retain seats in the parliament with a disappointing result of 4.8 percent, falling short of the 5-percent minimum support to enter parliament, the official provisional results showed.

Its leader Philipp Roesler, who served as economy minister and deputy chancellor in the coalition government, offered to step down from the party post Monday.