A senior member of Libya's Muslim Brotherhood has conceded that its Justice and Construction party had fallen short of expectations, after early election results gave victory to its more secularist rival, the National Democratic Alliance (NDA).

The bulk of results from Saturday's election, the first held in Libya since the fall of Muammar Gaddafi last year, have still to be announced but after two crushing victories, NDA officials claim they will emerge as the largest party.

"We had an expectation before the election, we have not reached that expectation," said the Justice and Construction party's campaign manager Alamin Belhaj, who is also a member of Libya's ruling National Transitional Council, which is due to hand over to the new parliament in the coming weeks.

Belhaj, a businessman who lived with his wife and children in Manchester until returning for last year's revolution, accused NDA leader Mahmoud Jibril of using unfair campaign practices for his victory, saying Jibril's picture should not have appeared on campaign material as he was not himself running for office.

"Jibril is not a candidate, while his pictures are up all over the country, its a way of tricking people."

Jibril, a former economic planner in the Gaddafi regime who worked closely with the dictator's son, Saif al-Islam, to design a reformist constitution that was never implemented, has proved a popular choice with voters: in the western Tripoli suburb of Janzour, the NDA won 26,000 votes, compared to 2,400 for the Brotherhood.

On Sunday, Jibril offered to work with all parties in a coalition government, but Belhaj ruled any co-operation out. "No, no, he did not invite us, so we do not invite him," he said.Although Libya's election commission has confirmed results for only three districts, election tallies have been available at polling stations, leading to claims from the NDA that it has won huge majorities in both Tripoli and Benghazi, Libya's second city.

Many had expected the Brotherhood to repeat the successes seen in Egypt and Tunisia earlier this year.

"We all predicted, we were wrong. I thought they [the Brotherhood] would do better, particularly here in Tripoli, because if you look back they were relatively organised," said Dirk Vanderwalle, an American politics professor who worked until a few weeks ago on the staff of UN special representative to Libya Ian Martin.

Victory in local elections in Benghazi in May seemed to confirm that the Brotherhood would do well in Libya.

Belhaj, who is due to travel to Cairo on Wednesday to congratulate Egypt's president, Mohammed Morsi, on behalf of the NTC, on his election win last month, blamed the poor image of the Brotherhood spun by the Gaddafi regime for the poor showing in the polls. "Libyans have had 40 years of Gaddafi saying the Brotherhood are agents. Its not easy to change the mind. Our problem is we have not yet touched the heart of the people."