President-elect Enrique Peña Nieto's Institutional Revolutionary Party, or PRI, ended up with the most seats in Congress, based on an analysis of the "probable composition" of the next legislature, the Federal Electoral Institute, or IFE, said.
The PRI, if the election results are certified, will have 207 seats in the 500-member lower house of Congress, while the conservative National Action Party, or PAN, will hold 114 seats and the leftist Party of the Democratic Revolution, or PRD, will have 101, the IFE said.
The Mexican Green Party, an ally of the PRI, will have 33 seats in the lower house of Congress.
The Workers Party and the Citizens Movement, both members of the leftist coalition, will have 19 seats and 16 seats, respectively, while the New Alliance Party, or PANAL, will have 10 seats.
The PRI will have 52 of the 128 seats in the Senate, while the PAN will hold 38 seats and the PRD will have 22 seats.
The Green Party will have nine seats, the Workers Party will hold four seats, the Citizens Movement will have two seats and PANAL will have one seat, the IFE said.
"These are the results that the IFE has processed up to this point and, in any case, they must be certified by the High Chamber of the Elections Tribunal of the Judicial Branch of the Federation (TEPJF), which has the final say on electoral matters," the elections agency said in a statement.
The PRI will not have enough seats in Congress to push through the structural reforms promised by Peña Nieto during the campaign to bolster Mexico's economy.
Peña Nieto won the presidency with 38.21 percent of the vote, while Lopez Obrador took second place with 31.59 percent, according to the final official results released by the IFE.
Lopez Obrador said the electoral courts would be asked on Thursday to annul or declare the July 1 presidential election invalid on the grounds that 5 million votes "were bought" for the PRI.
The results are subject to challenge under Mexican elections law. EFE