Aya Hijazi, founder of a charity that promotes a better life for street children, has returned to the US after three years in an Egyptian jail.

An Egyptian American charity worker who was imprisoned in Cairo for three years and became the global face of Egypt's brutal crackdown on civil society returned home to the United States after the Trump administration quietly negotiated her release.

President Donald Trump and his aides worked for several weeks with Egyptian President Abdel Fatah al-Sissi to secure the freedom of Aya Hijazi, 30, a US citizen, as well as her husband, Mohamed Hassanein, who is Egyptian, and four other humanitarian workers. Trump dispatched a US government aircraft to Cairo to bring Hijazi and her family to Washington.

Hijazi was working in Cairo with the Belady Foundation, which she and her husband established as a haven and rehabilitation centre for street children in Cairo.

MOHAMED ABD EL GHANY Aya Hijazi's husband Mohamed Hassanein and four other humanitarian workers were also released.

The couple and their co-workers had been incarcerated since May 1, 2014, on child abuse and trafficking charges that were widely dismissed by human rights workers and US officials as false. Virtually no evidence was ever presented against them, and for nearly three years they were held as hearings were inexplicably postponed and trial dates cancelled. Human rights groups alleged that they were abused in detention.

The Obama administration unsuccessfully pressed Sissi's government for their release. It was not until Trump moved to reset US relations with Egypt by embracing Sissi at the White House on April 3 - he publicly hailed the autocrat's leadership as "fantastic" and offered the US government's "strong backing" - that Egypt's posture changed. Last Sunday, a court in Cairo dropped all charges against Hijazi and the others.

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SUPPLIED Egypt's President Abdel Fattah al-Sissi met US President Donald Trump in the White House in April this year, signalling a thawing of relations.

What the White House plans to celebrate as vindication of its early diplomacy comes at the end of a week in which the administration has combated charges of foreign policy confusion. Although the president received wide praise for his decision to punish Syria for its presumed chemical weapons attack with a barrage of cruise missiles, the administration has been criticised for contradictions over policy toward Syria and Turkey, and misstatements on the US response to North Korea's weapons activity.

A senior administration official said that no quid pro quo had been offered for Hijazi's release but that there had been "assurance from the highest levels [of Sissi's government] that whatever the verdict was, Egypt would use presidential authority to send her home." The official said the US side interpreted that to mean that a guilty verdict and sentencing would be followed by a pardon from Sissi, but they were pleasantly surprised.

The dropping of charges set in motion the release of Hijazi and Hassanein from custody and their journey to the United States, which was personally overseen by Trump and detailed on Thursday (local time) by the senior administration official, who spoke on the condition of anonymity because of the national security sensitivities of the case.

Defence Secretary Jim Mattis and deputy national security adviser Dina Powell, who were already planning to visit Egypt this week and met with Sissi on a range of topics. Meanwhile, Trump also sent his military aide, Air Force Major Wes Spurlock, to escort Hijazi and her family on the plane home to Washington.

Hijazi and Hassanein reunited with the Hijazi family in Cairo this week, and as Mattis travelled on to Israel, Powell, who was born in Egypt and has helped smooth relations between the two countries, stayed behind to accompany the group, the senior administration official said.

The travellers touched down at Joint Base Andrews about 10 pm on Thursday. Hijazi and her brother, Basel, are scheduled to visit the White House on Friday to meet with Trump and his daughter, Ivanka, and his son-in-law, Jared Kushner, who had followed Hijazi's plight, the senior administration official said.

"It's been a roller coaster of emotions the past couple of days," Basel Hijazi said in a telephone interview Thursday from aboard the plane. "We're crying with relief to have them out."

He added: "We're very grateful that President Trump personally engaged with the issue. Working closely with the Trump administration was very important for my family at this critical time. It let us be reunited as a family. We're so grateful."

Since Sissi came to power in a 2013 coup, his authoritarian government has presided over a lurching economy, with massive debt, high unemployment and allegations of corruption. A US$12 billion (NZ$17 billion) loan last year from the International Monetary Fund and strict austerity measures have led to slow improvements, but Egypt still needs major outside investment and favourable financing.

Sissi, a former army chief who led the coup that overthrew Egypt's elected president, had been barred from the White House by the Obama administration for human rights abuses. Sissi's post-coup crackdown has been particularly severe against civil society groups, especially those receiving money from abroad. They are frequently denounced by the government and pro-government media as trying to destabilise the country. Thousands of people remain imprisoned.

While President Barack Obama was uneasy with the elected government of Mohamed Morsi, whose political organisation was tied to the Muslim Brotherhood, his administration rejected Sissi's charges of terrorism ties. After the coup, Obama withheld aid from Egypt - for decades, the second-largest recipient of US military assistance, after Israel, at more than US$1 billion a year.

During his presidential campaign, Trump expressed admiration for authoritarian leaders he felt were tough on terrorism and derided what he called Obama's "weak" leadership.

This month, as Sissi smiled beside him in the Oval Office, Trump said warmly: "We agree on so many things. I just want to let everybody know, in case there was any doubt, that we are very much behind President al-Sissi."