Nigeria's parliament has stepped up pressure on President Olusegun Obasanjo, who has been fighting calls by lawmakers who want him to resign.

The Nigerian Senate on Tuesday passed a measure to expand an ongoing investigation of President Obasanjo a move that some observers say is another step towards impeachment proceedings against the Nigerian leader.

The investigation seeks to expose why President Obasanjo's administration has not implemented budgets passed by the National Assembly since 1999.

It is this same issue that two weeks ago prompted legislators in the lower chamber to call on Mr. Obasanjo to step down. Members of the House of Representatives, including members of Mr. Obasanjo's own People's Democratic Party, gave the president two weeks to resign or face impeachment, accusing his administration of corruption and incompetence.

The ultimatum expired Monday.

Members of the lower chamber met on Tuesday and set up a panel to come up with a resolution on whether to go forward with impeachment efforts. The matter will be taken up again when the House of Representatives meets at a regular session on September 4.

Over the past two weeks, supporters of Mr. Obasanjo have been meeting with his opponents in the National Assembly for what observers say have been intense negotiations. Last week, 14 House members said they had decided to abandon the impeachment effort.

On Sunday, President Obasanjo appeared on national television, saying he was confident the crisis had passed.

Observers say it is unlikely that President Obasanjo will be forced to resign. They say the impeachment threats, which are nothing new, are an attempt by his opponents to damage him politically as he prepares to run for reelection next year.

Mr. Obasanjo was elected in 1999, ending more than 15 years of military rule in Nigeria Africa's most populous nation. Challenges facing his government have included rising poverty and festering tensions between Muslims and Christians over the implementation of the Islamic justice code, Sharia, in some northern states.