COLOMBO (AFP) - Sri Lanka's new president has axed hundreds of officials and diplomats appointed by his predecessor as he prepares to form his new Cabinet, a senior aide said Monday.

Lawmaker Rajitha Senaratne also said President Maithripala Sirisena would announce his Cabinet later Monday.

"He has asked all political appointees of the former president to resign immediately," said Senaratne, adding politically appointed diplomats had been asked to return to the country.

"We are going to have a Cabinet of 29 ministers," Senaratne told AFP.

Sirisena invited all parties to join his cabinet on Sunday, two days after ousting Sri Lanka's longtime leader Mahinda Rajapaksa in a surprise election victory.

The new president quit Rajapaksa's Cabinet in November to emerge as an opposition unity candidate in the Jan 8 polls, triggering a mass defection of lawmakers.

Analysts have already warned that he may struggle to satisfy the diverse coalition that backed his campaign.

As he got to work on Monday, Sirisena spoke to top US diplomat John Kerry after pledging to mend ties with the West.

The US secretary of state said Washington wanted to strengthen its relations with Sri Lanka, which soured under Rajapakse.

Senaratne said the new government had secured wide support, including from parties outside the coalition.

The main party representing the country's Tamil minority, who played a significant role in ousting Rajapakss, declined to take any Cabinet positions but agreed to support the president, Senaratne said.

Sirisena, who needs a majority in the 225-member assembly to push through ambitious reforms, has moved to strengthen his hold on parliament by securing further defections.

He has pledged to reverse many of the constitutional changes made by the former president, who gave himself huge powers over all key institutions, including the judiciary.

Rajapaksa's Sri Lanka Freedom Party (SLFP) split on Sunday night when a section of its policy-making central committee broke away and pledged support to Sirisena.

Sirisena loyalist Duminda Dissanayake said the SLFP had appointed the new president as party leader, though that was immediately challenged by the Rajapaksa camp.

The new president has already led the biggest defection from any government in Sri Lanka since independence from Britain in 1948.