BEITBRIDGE, Zimbabwe (AP) - Zimbabwean President Robert Mugabe celebrated his 84th birthday Saturday at a rally aimed at boosting support before elections next month.

The bash in the southern town of Beitbridge on the border with South Africa cost 3 trillion Zimbabwe dollars - the equivalent of about US$250,000 or euro170,000 at the dominant black market exchange rate.

A laughing Mugabe, wearing a garland of flowers and surrounded by supporters, was seen punching the air with his fists.

He hit out at the country’s "enemies" who have criticized his presidency, including the U.S. and Britain.

"There will never be regime change here ... Never," he said.

While the autocratic leader, one of Africa’s longest rulers, was eating cake, his country faces its worst political and economic crisis with inflation rocketing past the 100,000 percent barrier this week.

Across the border, a few hundred Zimbabweans held a protest in the South African town of Musina. They launched a giant helium balloon with banners reading: "Elections free and fair or just hot air?" and "Bob, you’ve had your cake. Now beat it."

Mugabe faces his greatest electoral challenge since he led the nation to independence in 1980. The presidential vote on March 29 is being contested by former ruling party loyalist Simba Makoni and the leader of an opposition faction, Morgan Tsvangirai, who launched his campaign in the eastern town of Mutare on Saturday.

In a nationwide television broadcast Thursday to mark his birthday, Mugabe verbally attacked Makoni, 57, calling him a "prostitute" and a "deviant" from the ruling party principles that built the country.

He could face a run off presidential poll for the first time if he does not win 51 percent of the vote.

Makoni, fired by Mugabe as finance minister in 2002 in disagreements over economic policy, is expected to attract votes from disillusioned members of the ruling party and the fractured opposition.

Economic hardship is a key issue in the national elections. The former regional breadbasket is facing acute shortages of food, hard currency, gasoline and most basic goods.

The economic meltdown is blamed on disruptions in the agriculture-based economy after the often-violent seizures of thousands of white-owned commercial farms began in 2000 accompanied by political violence and turmoil.

The state central statistical office has said the official rate of annual inflation rose to 100,580 percent in January - the highest in the world.

The new official figure was still well below the rate calculated by independent analysts who estimate real inflation is closer to 150,000 percent.