More than 3,000 customs employees in the oil-rich Gulf state of Kuwait went on strike on Monday demanding better pay and paralyzing exports and imports, a trade union official said.

"The strike is total as all of the more than 3,000 customs employees have stopped work. We are on an indefinite strike until our demands are met," Fahhad al-Ajmi, board member of the customs trade union, told Agence France Presse.

OPEC member Kuwait is bracing for a major political showdown over a graft scandal involving MPs as the opposition mounts a fierce campaign to oust the prime minister.

Liberal, nationalist and Islamist opposition groups have united following allegations that pro-government MPs accepted hundreds of millions of dollars in bribes, with fingers pointed at the government as the source of the money.

Four workers were killed and two employees injured in a gas pipe explosion on Saturday at Kuwait's largest refinery of Mina al-Ahmadi, Kuwait national refiner said.

The explosion took place at the Gas Liquefaction Plant at the refinery during maintenance works, Kuwait National Petroleum Co (KNPC) said in a statement cited by the official KUNA news agency.

U.S. Vice President Joe Biden met Thursday at the White House with Kuwaiti Prime Minister Sheikh Nasser Mohammad al-Ahmad al-Sabah for talks on the Arab Spring and the emirate's thorny ties with Iraq.

The pair discussed a range of issues, "including the changes underway in the region as a result of the Arab Spring, and the importance of resolving outstanding issues between Kuwait and Iraq," the White House said.

The public prosecutor in OPEC member Kuwait has expanded an unprecedented probe into the bank accounts of several MPs suspected of receiving illegal deposits, local media reported on Thursday.

Citing unnamed sources, al-Jarida daily said the bank accounts of four more MPs were referred to the public prosecution, raising the number of lawmakers under investigation to 14.

A Kuwaiti court on Sunday sentenced a Sunni Islamist activist to three months in jail for writing remarks on his Twitter account deemed derogatory to Shiite Muslims, a legal source said.

Mubarak al-Bathali, who is serving another three-month jail term on a similar case, was arrested several weeks ago by the secret service police on charges of undermining national unity and disparaging Shiites.

Kuwaiti opposition groups called a rally for Wednesday to press for the government's resignation over an alleged corruption scandal involving a number of MPs and possibly former ministers.

The rally, called by Islamist, liberal and nationalist groups who altogether have more than 20 MPs in the 50-seat parliament, will kick start a campaign to expose those who paid and received the money and for what purposes.

A Kuwaiti political group and two youth groups said Wednesday they solidly back calls for a constitutional monarchy as the wealthy Gulf state battles with a corruption scandal involving MPs.

A call for fundamental political reforms, including the appointment of a premier from outside the ruling family, was made on Sunday by the September 16 Youths group which plans to stage a major rally on Friday to press for change.

Kuwaiti youth activists called on Sunday for major reforms to turn the oil-rich emirate into a constitutional monarchy, including the appointment of a premier from outside the Al-Sabah ruling family.

The previously unknown September 16 Youths group also called for the dismissal of the current government, the dissolution of parliament and the holding of fresh elections.

The wealthy Gulf state of Kuwait appeared headed Thursday for a major political crisis over allegations of corruption involving several members of parliament and former ministers.

Media reported that a number of banks planned to refer as many as 15 MPs and possibly former ministers to the public prosecution to investigate "suspicious" huge cash deposits into their accounts.