KUALA LUMPUR (Reuters) - Malaysian Prime Minister Najib Razak reshuffled his cabinet on Monday, placing party loyalists in top posts in a bid to strengthen the ruling coalition amid speculation that he could call an early election next year.

Landslide victories in recent electoral outings have put the scandal-hit Najib and his ruling alliance, Barisan Nasional, in a position of strength, and the new cabinet appointments are seen as a move to build on that.

"This will strengthen the current administration further to ensure the government's development agenda for the people - economic, welfare and security development - will continue smoothly as promised," Najib told a news conference.

A source within the ruling administration told Reuters that the strong results in Sarawak state polls in May and two by-elections earlier this month were what Najib was waiting for to decide when he will call national polls, which will likely be by the second half of 2017.

The last cabinet reshuffle was in July 2015, when Najib dropped leaders critical of his handling of troubled state fund 1MDB.

Najib, who chaired the advisory board of 1MDB, has faced intense pressure following revelations that $681 million was transferred into his personal account. Najib has denied any wrongdoing.

Najib has faced calls to resign over the past year over 1MDB, which is being investigated for money-laundering in at least six countries including the United States, Switzerland and Singapore.

Of the new ministers, Mah Siew Keong, a senior ethnic Chinese politician and leader of the Malaysian People's Movement Party, was appointed as the new plantation industry and commodities minister.

Noh Omar, a veteran leader of the ruling United Malay National Organisation (UMNO), was appointed minister for urban wellbeing, housing and local government.

Second Finance Minister Ahmad Husni Hanadzlah quit his post due to "personal reasons" and was replaced by Johari Abdul Ghani.

Abdul Rahman Dahlan was put in charge of the Economic Planning Unit in the Prime Minister's Department.

(Reporting by Joseph Sipalan; writing by Praveen Menon; Editing by Nick Macfie)