"Israel's convoluted legal rules thwart Eritrean and Sudanese asylum seekers' attempts to secure protection under Israeli and international law," New York-based HRW said in a statement accompanying the 83-page report.
"Israeli authorities have... Denied them access to fair and efficient asylum procedures, and used the resulting insecure legal status as a pretext to unlawfully detain or threaten to detain them indefinitely, coercing thousands into leaving."
Israel has come under fierce criticism from rights groups for its immigration policy and treatment of African asylum seekers, particularly over its Holot detention centre where illegal immigrants can be held for up to a year.
"International law is clear that when Israel threatens Eritreans and Sudanese with lifelong detention, they aren't freely deciding to leave Israel and risk harm back home."
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Some of those returning to Sudan have faced "torture, arbitrary detention, and treason charges for setting foot in Israel," the report said.
In response to the HRW report, a spokeswoman for Israel's population and migration authority defended its policy as "proportionate" and said the numbers of those leaving voluntarily had increased threefold since 2013.
The UN says there are some 53,000 refugees and asylum-seekers in Israel, most of whom entered via the desert border with Egypt.
Of that number, some 36,000 come from Eritrea where the regime has been repeatedly accused of widespread human rights abuses. Another 14,000 are from conflict-torn Sudan.
"Destroying people's hope of finding protection by forcing them into a corner and then claiming they are voluntarily leaving Israel is transparently abusive," Simpson said.
Israel opened the Holot detention camp in the southern Negev desert last year as part of a crackdown on illegal immigrants, with the facility open by day but locked down at night.