Ammon News - DUBAI (Reuters) - Moderate cleric Hassan Rohani took a commanding lead ahead of conservative rivals in Iran's presidential election, according to initial results, but his tally appeared narrowly insufficient to avoid a second round run-off on June 21.

With about 5 percent of the votes counted, the former nuclear negotiator appeared to have benefited from a late surge in support among liberal Iranians attracted by his progressive policies.

Under the election rules, a candidate has to win more than 50 percent of the total votes cast to win outright. A first round winner gaining less than that must compete with the runner-up in a second round a week later.

Rohani has about 45 percent of the votes so far.

Voting was extended by several hours at polling stations across the country on Friday as millions of Iranians turned out to cast their ballot in the first presidential race since a disputed 2009 contest led to months of political unrest.

Of the 1,819,984 votes counted so far, Rohani received 834,859, with his closest competitor, Tehran Mayor Mohammad Baqer Qalibaf, getting 320,562 votes, an election official announced live on state television.

In third place was Iran's chief nuclear negotiator, Saeed Jalili, with 257,822 votes, followed closely by Mohsen Rezaie, a former head of the elite Revolutionary Guard, with 214,368 votes.

Trailing the field were former Foreign Minister Ali Akbar Velayati with 106,144 votes, and little-known former minister Mohammad Gharazi with 25,324 votes.

The election is unlikely to radically alter ties between the West and the OPEC member nation of 75 million, but could tone down the confrontational style favored by current president Mahmoud Ahmadinejad.

World powers in talks with Iran over its nuclear program are looking for any signs of a readjustment of its negotiating stance after eight years of intransigence.

Security has been tight and campaigns subdued compared to the euphoric rallies that preceded the last presidential election in 2009, when reformist supporters thought they scented victory and the prospect of change in Iran.

Those hopes were dashed when rapid announcements gave Ahmadinejad 63 percent of the vote, returning him to office and starting a series of deadly protests that lasted for months.

Rohani received significant boosts earlier this week when reformist candidate, Mohammad Reza Aref, withdrew in his favor. His campaign was also endorsed by former presidents Mohammad Khatami and Akbar Hashemi Rafsanjani.

In contrast, Iran's big-hitting conservatives failed to organize themselves around a unity candidate, suffering what appeared a decisive split in their support base as a result.