WASHINGTON (REUTERS) - The messages from Alan Gross had grown increasingly ominous. In May, on his 65th birthday, the former US aid worker said he would rather die than spend another birthday in a Cuban prison.

Two weeks ago, his wife said he was "literally wasting away."

But arriving home on Wednesday, Gross - released after more than five years of imprisonment on espionage charges - looked almost giddy with joy as he told a news conference in Washington he was "incredibly blessed" to be free.

Gross's emotional homecoming opened the way for US President Barack Obama to announce he will restore diplomatic relations with communist Cuba after half a century of estrangement.

Such a move was seen as all but impossible while Gross was still jailed.

"I'm free" were the first words Gross said to his two daughters when he called each of them from the plane after leaving Cuban airspace, a family spokesman said.

Cuba arrested Gross on Dec 3, 2009, and later sentenced the US Agency for International Development (USAID) contractor to 15 years in prison for importing banned technology and trying to establish clandestine Internet service for Cuban Jews. He was working for Maryland-based Development Alternatives Inc.

Gross, who some reports said had grown increasingly embittered towards the Obama administration for not doing more to win his release, had nothing but praise for the president.

"Ultimately, the decision to arrange for and secure my release was made in the Oval Office," he said.

A long-time supporter of Jewish causes and a development consultant who had travelled the world, Gross, who had little experience in Cuba and spoke little Spanish, maintained that he was guilty of nothing more than naivete.

During five trips to Cuba in 2009, he imported banned satellite communications devices and other gear in his luggage and helped install it at Jewish centres around the country. He was arrested just before he planned to return home.

Gross' case raised alarm about USAID's practice of hiring private citizens for secretive assignments abroad.

It took 18 months of secret negotiations to negotiate Gross' release and his deteriorating health added urgency to the talks.

In April, he went on a nine-day hunger strike. When he turned 65 in May, Gross vowed not to spend another birthday in prison, telling visitors he would rather die.

His spirits dimmed after his mother died of cancer in June, and he stopped seeing doctors, his wife or officials of the US interests section shortly thereafter.

"After five years of literally wasting away, Alan is done," his wife, Judy Gross, said in a statement on Dec 3. She described him as gaunt, hobbling and missing five teeth.

His lawyer, Scott Gilbert, said recently he had grown suicidal and lost about 45 kg.

He was told only on Tuesday that he was to be freed, in a phone call with Gilbert, family spokesman Jill Zuckman said.

"There was a long silent pause, and then Alan said, 'I'll believe it when I see it'."

On the flight home, Gross, in a phone call with Obama, thanked him for securing his release and said he was "grateful for the change in American policy towards Cuba", according to Chris Van Hollen, the congressman who represents Gross' Maryland district and who was on board.

On the plane, Gross was treated to a bowl of popcorn and a corned beef sandwich, his favourite. He also ate potato latkes, a traditional dish for the Jewish holiday of Hanukkah.

He was feisty when he took the podium briefly at his lawyer's office in Washington. He said nothing about his health, except when he pointed out that he needed dental work and then opened his mouth in a grin to display missing front teeth.