Tensions escalated further on Wednesday when an unknown armed man attacked the headquarters of Turkey's secular higher education board (YOK).
The man fired three shots before escaping, but no one was hurt.
YOK officials said the man had tried to forcibly enter the office to see Erdogan Tezic, a staunch secularist who has often clashed with the AK Party.
On Wednesday, Gul held talks with the True Path Party and independent MPs in a rare conciliatory move.
The True Path Party and ANAP, parliament's third largest party, said they would hold more talks before deciding on what position to take on Friday.
|Secular Turks held a huge rally on|
April 14 in Ankara to oppose an
Erdogan presidency [EPA]
Gul said: "I told them 'if parliament approves my candidacy and picks me as president ... I am aware of the responsibility of overcoming the difficulties which emerge from (the fact that) Turkey is a very politicised society'."
Analysts and diplomats say they see little risk that Gul would not win the presidential vote because of the AK Party's control of parliament with 354 seats out of 550.
But the party needs the attendance of the two opposition parties in the chamber during the vote to help stave off the CHP's legal challenge.
The CHP insists at least two-thirds of deputies must be present or the vote will be invalid.
Turkey's powerful secular establishment, which includes army generals and judges, had campaigned hard to stop Tayyip Erdogan, the country's prime minister, from running for president.
They accuse him of harbouring a hidden Islamist agenda and seeking to undermine the republic's separation of state and religion.
Both Erdogan and Gul strongly deny the Islamist charges.
Turkey's leading newspapers, often at odds with the AK Party, have largely given Gul their support.
For its part, Tuisaid, Turkey's leading business association, has played down any threat Gul's election might pose to the secular system.
Meanwhile, Turkey's lira currency and sovereign bonds extended gains as investors signalled their approval of Gul.