KABUL: Afghan election front-runner Abdullah Abdullah received a major boost to his presidential campaign on Sunday with the endorsement of third-placed Zalmai Rassoul, a close ally of the current leader.
Rassoul was seen as the favoured candidate of outgoing President Hamid Karzai, and his support for Abdullah could be influential in deal-making to choose Afghanistan's next leader as US-led troops withdraw from the country.
Rassoul's own bid to become president gained little momentum and he took just 11.5 percent in the first round of voting.
"I ask the people for the sake of national unity and political stability to vote for Doctor Abdullah, so that we win the election," Rassoul, who resigned as foreign minister to run in the election, told a press conference in Kabul.
Rassoul said his support could be a "balance-maker" in the run-off vote due next month.
The second-round vote will pit Abdullah against former World Bank economist Ashraf Ghani, after the two came first and second in the eight-man election on April 5.
Neither candidate secured the 50 percent needed for outright victory, with Abdullah gaining 44.9 percent and Ghani on 31.5 percent, according to preliminary results.
The official final first-round result will be announced on Wednesday after weeks of adjudication over fraud complaints.
Karzai, who is constitutionally barred from a third term in office, stayed publicly neutral in the election, but his elder brother Qayum Karzai dropped out of the race before polling day and endorsed Rassoul.
It remained unclear on Sunday whether the Karzai family supported Rassoul joining the Abdullah camp.
"This is a big move in the modern history of Afghanistan," Abdullah, a former foreign minister, told supporters. "We are one team, a team committed to honesty and working sincerely to fullfil our commitments to the people."
The 2009 election, when Karzai retained power after defeating Abdullah, was marred by massive fraud in a chaotic process that shook the multinational effort to develop the country after the ousting of the Taliban regime in 2001.
The eventual winner will lead Afghanistan into a new era as US-led NATO combat troops end their 13-year war against the Taliban insurgency that erupted after Karzai took power.
The first-round election was hailed as a success by Afghan officials and foreign allies, with turnout far better than in 2009 and the Taliban failing to launch a major attack despite threats to disrupt the vote.
A run-off vote in June -- at the height of the traditional "fighting season" -- is likely to be more difficult for Afghanistan's stretched security forces to guard.
Another election could be avoided by negotiations in the coming weeks, but both Abdullah and Ghani have dismissed talk of a power-sharing deal.
"Rassoul's joining to Abdullah's team is very important. It will change the game toward Abdullah," author and analyst Ahmad Saeedi told AFP.
"Rassoul does not want to be left out of the whole game, he wants to stay in the government somehow and with Abdullah he will be there."
Abdullah secured another useful ally 10 days ago when another candidate, Gul Agha Sherzai, pledged his support.
Sherzai, who took just two percent of the vote on April 5, is seen as able to deliver some support from Pashtuns, the country's largest ethnic group.
Abdullah's support is strongest in Tajik ethnic areas due to his role as a close adviser to the late Ahmad Shah Massoud, a revered Tajik leader who fought the Taliban during their 1996-2001 rule.