Prime Minister Jadranka Kosor, who also succeeded Sanader in his post as leader of the centre-right HDZ (Croatian Democratic Union) party, said his attempt to return to politics was a move to topple the government and create chaos at a decisive moment for the country's EU accession, the Croatian agency HINA reported.
Sanader unexpectedly resigned in July 2009 in the middle of his second term. He offered no explanation for his departure. Kosor expelled Sanader from HDZ.
Before returning to Croatia on 3 October Sanader was an associate lecturer at the Harriman Institute at Columbia University in New York.
Sanader won his parliamentary seat in 2007 elections, but it was held by a member of the ruling party while he served as prime minister.
Experts believe that Sanader has two reasons to return to politics: either, indeed, to seek to topple Jadranka Kosor's government, or to win temporary immunity from prosecution for crimes for which he is under investigation, dating back to his time as prime minister.
Sanader was questioned earlier this week about the circumstances under which Hungarian company MOL gained a controlling stake in Croatian oil company INA.
Some of the former prime minister's closest aides have been detained and accused of corruption. Local media speculate that the arrests may be a signal that charges against Sanader are imminent.
After Sanader's resignation, Kosor launched a crackdown on corruption that won praise from the European Union, which Croatia hopes to join soon.
Next Wednesday, The parliamentary credentials and privileges commission (MIP) will consider Sanader's request in order to establish whether it is in line with the law.
After that, the commission should inform the parliament about its decision, which is to be endorsed at the parliament's plenary session.
