WASHINGTON - REPUBLICAN Senator John McCain expressed support for his former presidential running mate, Sarah Palin, on Saturday as Washington speculated about why the Alaska governor abruptly announced her resignation.

Mr McCain made the comment a day after Ms Palin stunned the political world by announcing she is stepping down with 18 months left in her term.

Mr McCain had plucked Ms Palin from obscurity to make her his vice presidential running mate in last year's presidential campaign, won by Democrat Barack Obama.

'I have the greatest respect and affection for Sarah, Todd, and their family. I was deeply honoured to have her as my running mate and believe she will continue to play an important leadership role in the Republican Party and our nation,' Mr McCain said in a statement e-mailed to Reuters.

But Alaska's Republican Senator Lisa Murkowski issued a statement saying, 'I am deeply disappointed that the Governor has decided to abandon the State and her constituents before her term has concluded.' Ms Palin defeated Mr Murkowski's father, then-Governor Frank Murkowski, in the 2006 Republican primary for governor.

A polarising figure who is mainly popular among conservatives, Ms Palin has often been considered a contender for the Republican presidential nomination in 2012.

Her decision, announced in a rambling, disjointed statement in her home town of Wasilla, Alaska, fueled speculation that she might be seeking to position herself for a run.

But some commentators said it was a strange move for one with presidential ambitions, opening her to potential criticism that she quit her post to pursue a personal agenda.

In her statement, Ms Palin referred to a series of ethics probes into her conduct as governor and previously as mayor of Wasilla, all of which she said lacked merit.

'My staff and I spend most of our day dealing with this instead of progressing our state now,' Ms Palin said. 'This isn't what anyone had in mind for Alaska.' Palin's lawyers released a statement on Saturday denying allegations her resignation was linked to a criminal investigation on construction of a sports complex in Wasilla. -- REUTERS