President Robert Mugabe, 93, has refused to name a successor in next year's presidential election

President Robert Mugabe on Friday accused a recently launched opposition alliance seeking to unseat him in next year's elections of plotting with Western powers to force him out.

Morgan Tsvangirai, the leader of the country's main opposition party the Movement for Democratic Change (MDC), formed a grand coalition last month with former allies and four opposition parties in an effort to end Mugabe's 37-year rule.

"Recently we have witnessed the concerted effort by opposition political parties to coalesce and fight (us) as one," Mugabe, 93, said at a meeting of his ZANU-PF party's central committee in Harare.

"We know of course they are a creature of the West whose sole purpose is to dislodge ZANU-PF from power, but really if they come together as a bundle, one blow will set the bundle in pieces.

"Fortunately for ZANU-PF, the political parties are as divided as ever, fighting over political positions."

A planned pact between Tsvangirai and Mugabe's former vice president Joice Mujuru failed following disagreements over leadership.

Tsvangirai has made three failed bids for the presidency.

In 2008, he beat Mugabe in the first round of voting but failed to win an outright majority, leading to a run-off. He later pulled out of the second ballot as violence against his supporters raged.

Past elections in Zimbabwe have been marred by violence, intimidation and charges of electoral fraud.

The president, who often travels abroad for medical treatment, has refused to name a successor and repeatedly denounced factionalism within his own party.