KABUL, Afghanistan (AP) — Afghan presidential candidate Abdullah Abdullah defiantly told thousands of supporters Monday that he will declare victory as he claimed massive fraud was responsible for preliminary results putting his rival in the lead. The United States, meanwhile, warned both camps against trying to seize power, saying international financial and security support was at stake.

The turmoil came as violence escalated around the country. A suicide bomber struck Afghan and foreign forces near a clinic in the eastern province of Parwan, killing at least 16 people, including four Czech soldiers.

Abdullah said he received calls from President Barack Obama and U.S. Secretary of State John Kerry, and he was told that Kerry would be flying to the Afghan capital on Friday in a bid to help defuse the crisis. State Department officials accompanying Kerry in Beijing declined to comment on his travel plans.

Abdullah told his supporters that the results of the election were fraudulent, but asked them to give him a few more days to negotiate.

"We denounce and do not accept the results of the fraudulent vote. I assure you people of Afghanistan that I will sacrifice for you, but I will never accept a fraudulent government," he told his supporters, many angry over the result. "We announce that only the government elected through clean votes will come to power."

The Afghan Independent Election Commission released preliminary election results Monday showing former finance minister Ashraf Ghani Ahmadzai well in the lead for the presidency but said no winner could be declared because millions of ballots were being audited for fraud.

Preliminary results from the June 14 runoff vote announced Monday showed that Ahmadzai had about 4.5 million votes, or 56 percent, while Abdullah had 3.5 million votes, or 44 percent, according to the commission. Turnout was more than 50 percent.

That was a sharp turnaround from the first round of voting on April 5 when Abdullah garnered the most votes with 46 percent to Ahmadzai's 31.6 percent but failed to get the majority needed to avoid a runoff vote.

Abdullah has refused to accept any results from the second round until all fraudulent ballots are invalidated.

Ahmadzai, a U.S.-educated former finance minister and World Bank official, said he also had spoken to Kerry on the telephone.

"We welcome him (Kerry) coming here, but the real responsibility is up to us and we are hopeful that we will fulfill all our responsibilities," he said at a news conference at his home in Kabul. "We are prepared to engage in political discussion in order to make sure that we move to insure the legitimacy of the process, its fairness and the acceptance of its results."

He also rejected the idea of parallel governments, which has been raised by some Abdullah supporters.

"Talk of parallel governments will remain in the level of talk, because the historic responsibility that his excellency Dr. Abdullah and I as people who have submitted ourselves to the will of the people of Afghanistan have is to ensure the stability of this country and the legitimacy of the regime to which we have devoted our lives."

The election commission acknowledged that vote rigging had occurred and said ballots from about 7,000 more of the nearly 23,000 polling stations would be audited.

Abdullah charged that outgoing President Hamid Karzai, Ahmadzai and the election commission were colluding against him. "They ignored us and announced the fraudulent results," he said.

There were fears that Abdullah could ignore the result and declare victory, something he hinted at during his speech.

"People across the county call on us to announce our government and I can't not say no to people's wish, we don't want civil war, we don't want crisis. All of our lives we defended this country. We do not want crisis, we want national unity," Abdullah said. "We don't want separation, we don't want civil war."

"We are the winner of the election without any doubt," he said, but called on his supporters to give him a few days to find a solution.

U.S. Secretary of State John Kerry said during a visit to Tokyo that any action to seize power illegally in Afghanistan would lead to the end of U.S. financial and security support.

Kerry said suggestions of a "parallel government" in Afghanistan were a grave concern and added that he expected Afghan electoral institutions to conduct a full review of all reasonable allegations of irregularities. He said there was no justification for violence or threats of illegal action.

"Any action to take power by extra-legal means will cost Afghanistan the financial and security support of the United States and the international community," Kerry said.

Abdullah said Obama had called him to promise help "in cleaning up votes."

Meanwhile, the Czech Ministry of Defense confirmed that four Czech troops were killed and another was badly wounded by Tuesday's blast.

At least 10 civilians and two police officers also were killed in the attack near the provincial capital of Charakar, local government spokesman Wahid Sediqqi said.

The Taliban claimed responsibility for the attack in a statement sent to the media.