Kuwait's premier and a senior royal filed two separate lawsuits to the attorney general on Monday demanding an investigation into allegations of a coup plot and a huge corruption scandal.
The wealthy Gulf state was shaken two months ago after news surfaced about videotapes allegedly showing former senior officials plotting a coup against the government.
This was followed last week by allegations of massive corruption by ex-government officials.
Prime Minister Sheikh Jaber Mubarak Al-Sabah sent a letter to the attorney general demanding an investigation into "allegations of money laundering, abuse of public funds and (financial) dealing with Israel," made during a television interview, acting Justice Minister Sheikh Mohammad Abdullah Al-Sabah told state news agency KUNA.
The accusations were made by Sheikh Ahmad Fahad Al-Sabah, a senior member of the ruling family, on Saturday.
Sheikh Ahmad, a former energy and economy minister, said he has material evidence senior ex-officials plotted a coup and stole tens of billions of dollars (euros) of public funds.
He has filed a lawsuit over the alleged conspiracy and corruption and handed over the evidence he had collected including videotapes showing the former officials conspiring, his lawyer Falah al-Hajraf said on Twitter on Monday.
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The government said in April the videotapes had been tampered with and were not authentic. But Sheikh Ahmad said in the interview he had won a ruling from a Swiss arbitration authority which was later attested by the British Supreme Court that the videotapes were genuine.
Later on Monday, an opposition group of former parliamentarians labelled the allegations "the most serious corruption case in Kuwait's modern history," and called for an international probe in a statement.
They also called for the government to be sacked, parliament dissolved and snap elections held on the basis of the pre-December 2012 electoral law. They demanded all officials suspected in the case should be dismissed and held accountable.
The developments come after similar allegations made at a public rally last week by prominent opposition members that former high-ranking officials had stolen around $50 billion and deposited them in foreign banks, including in Israel.
The government said on Monday it plans to file a lawsuit against the opposition leaders for the allegations they made against current and former officials, saying the accusations were not backed by evidence.
The Audit Bureau, the country's accounting watchdog, has been asked to launch a separate investigation into the allegations while the newly-established Kuwait Anti-Corruption Authority said Monday it will start its work by investigating the case.
Following months of relative calm that came after years of political disputes, OPEC member Kuwait was rocked by the two alleged scandals which threaten to plunge the emirate into a serious political crisis.
Kuwaiti opposition groups, which boycotted the last two election, in April called for democratic reforms including a Western-style party system and an elected government to limit the powers of the emirate's ruling Al-Sabah family which has been in power for over 250 years.