Pakistan has scheduled a presidential election on August 6 to replace incumbent Asif Ali Zardari.
The vote will be taken in the provincial and national parliaments.
Officials said on July 16 that Zardari's successor should be chosen no earlier than sixty days before and no later than sixty days after his five-year term expires on September 8.
Zardari is not seeking a second term because his Pakistan Peoples Party lacks the required number of lawmakers to win the vote.
Pakistan's Election Commission said the deadline to nominate candidates is July 24.
Prime Minister Nawaz Sharif's party, the Pakistan Muslim League-Nawaz, is expected to win because it has more lawmakers than any other party.
Zardari replaced former military ruler Pervez Musharraf in 2008 and served a full term despite strong opposition.
Based on reporting by DPA and BBC Urdu