By Natalia Zinets and Pavel Polityuk
KIEV (Reuters) - A senior Ukrainian prosecutor resigned on Monday, calling the office he worked for a "hotbed of corruption", another blow to government attempts to clean up the judiciary, a crucial step to unlock more Western aid.
The resignation, the second exit of a Western-backed reformer in under a fortnight, came a day before a possible no confidence vote in parliament that could topple Prime Minister Arseny Yatseniuk and lead to a snap election.
Failure to tackle endemic corruption has derailed a $40 billion aid program that keeps the war-torn country afloat. If Yatseniuk falls, it would further delay negotiations with the International Monetary Fund for the next tranche of money, $1.7 billion, which has been on hold since October.
"Today, the General Prosecutor's office is a brake on the reform of criminal justice, a hotbed of corruption, an instrument of political pressure, one of the key obstacles to the arrival of foreign investment in Ukraine," Deputy General Prosecutor Vitaliy Kasko said in a televised statement.
Kasko's move follows the exit of Economy Minister Aivaras Abromavicius, who accused vested interests, including a close ally of President Petro Poroshenko, of meddling in his ministry and trying to siphon off state funds.
Kasko's accusation that there was merely a facade of change in the prosecution service is damaging to Poroshenko, who has resisted pressure to fire General Prosecutor Viktor Shokin. Vladislav Kutsenko, an aide to Shokin, dismissed Kasko's resignation as self-publicity.
But U.S. Ambassador Geoffrey Pyatt called Kasko "a champion for change".
"His resignation is a blow to #Ukraine's reform progress ... #Ukraine deserves a clean judiciary. Will require top-to-bottom rule of law reform to address pervasive corruption + cronyism," he tweeted.
Yatseniuk's approval ratings have plummeted to less than 1 percent since he came to office in 2014 after protests ousted the previous pro-Russian government. The economy has tanked and a conflict with separatist rebels has no end in sight.
Parliament convenes on Tuesday to debate a report on the four-party coalition government's performance, which could precipitate a no confidence vote. A parliamentary source said that, after a meeting of various faction leaders on Monday, "the general mood is that the government should leave."
The prosecution service was hit by scandal last July when two high ranking officials were detained on suspicion of corruption and a large quantity of diamonds and money were found in raids on their homes.
(Writing by Matthias Williams; Editing by Robin Pomeroy)