The executive committee of the Social Democratic Party (SPD) in the German state of North Rhine-Westphalia (NRW) has said it does not intend to enter into a coalition with the Christian Democratic Union (CDU) of Chancellor Angela Merkel following the SPD's heavy defeat in state elections on Sunday.

"We accept this defeat. In view of the clear majorities, we are not available for a grand coalition," the party said in a statement on Monday evening.

The announcement paves the way for a coalition between the CDU and the Free Democratic Party (FDP) - known as a "black-yellow" coalition under Germany's political color coding system - although such a partnership would enjoy only a slim majority in the state parliament, holding 100 out of 199 seats.

"The CDU now has the task of forming a state government, and it has a majority for this with the FDP," the SPD statement said.

Read more here about the FDP.

A phoenix from the ashes

The FDP, which has seen its popularity fall drastically in the past few years, is currently undergoing a revival under its national leader Christian Lindner, who has also headed the FDP parliamentary party in NRW since the end of May 2012.

According to preliminary results, it received 12.6 percent of the vote at the NRW state election on Sunday, up from 8.6 percent in 2012 elections. The CDU, under its state leader Armin Laschet, gained 33 percent, jumping some 7 percent in comparison with 2012.

The SPD, the traditional ruling party in the heavily industrialized state, experienced its worst result since 1947 with 31.2 percent, as against 39.1 percent in 2012. Its state leader, Hannelore Kraft, announced her resignation from all party positions following the election disaster.

The election in the state is being seen as a key predictor for national elections on September 24.

Laschet himself said on Monday that he was open to partnerships both with the SPD and the FDP, which is currently in a coalition in the state of Rheinland-Palatinate - but with the SPD and Greens.

Read: Opinion: Time to risk something new

Black-yellow at national level?

With recent survey results showing the FDP gaining ground at the national level as well, leading CDU politicians are seeing a growing chance for a coalition between Merkel's conservative CDU/CSU bloc and the FDP following federal elections in September.

The FDP - which was the junior member of a coalition with the CDU from 2009 to 2013 - is seen by many as a natural coalition partner for the conservatives.

The election outcome in NRW had "refuted the claim that black-yellow is completely unable to attain a majority," CDU deputy leader Thomas Strobl told Tuesday's daily Handelsblatt, calling it "a good signal for the run-up to September 24."

Michael Fuchs, a deputy chair of the national CDU parliamentary party, also told the newspaper: "We want black-yellow."

Opinion polls still show, however, that the CDU and its Bavarian sister party the CSU, if they win the September elections, would need a third party to avoid a so-called "grand coalition" with the SPD, the combination currently in power.

A survey of national political sentiment published on Tuesday in the Bild newspaper showed the CDU/CSU and the FDP with 36 and 8 percent respectively, both up 1 percentage point from the week before. The SPD was on 27 percent, retaining its position. The populist Alternative for Germany also remained steady on 10 percent.