President Recep Tayyip Erdogan's ruling coalition partner on Tuesday backed the Turkish leader's surprise call to draft a new constitution, which some see as a bid to extend his rule.

Erdogan caught many off guard on Monday by suggesting that the "clear source of Turkey's problems" was its constitution being "written by putchists" following a 1980 military coup and in use since 1982.

He said he would push for a constitutional assembly if his junior partners in the ultranationalist MHP party support rewriting Turkey's basic law.

MHP leader Devlet Bahceli told reporters on Tuesday that it was "evident that Turkey needs a new constitution" and that his party was ready to join the process of writing it up.

Some analysts interpreted Erdogan's comments as part of a plan to extend his rule in the face of lagging public support.

The 66-year-old Turkish leader has headed the nation of 83 million people as prime minister or president since 2002.

His ruling AK Party pushed through constitutional changes in 2017 creating an executive presidency and eliminating the prime minister's post.

Erdogan then won his first of two potential five-year terms as president under the new rules in 2018.

Neither Erdogan nor Bahceli have fully explained why Turkey needs a new constitution or what the changes could entail.

But the Washington Institute think-tank's Turkey director Soner Cagaptay said they signalled Erdogan's recognition that he was losing public support.

Erdogan's popularity has been waning since he unleashed a sweeping crackdown after surviving a failed coup in 2016.

Accompanying economic problems have eroded support among working class voters who form a part of Erdogan's political base.

Cagaptay called the switch to a presidential system "perhaps Erdogan's greatest mistake in domestic politics to date" because it complicates his re-election chances.

"The presidential system requires a two-way race, at least in the run-off where two candidates compete against each other, which means that the system has unified Turkey's disparate opposition groups," Cagaptay told AFP.

Some Turkish media reports have suggested that Erdogan would like to keep the presidential system while making other changes whose details remain unclear.

Erdogan's rule under the current system could run until 2028 if he wins re-election in a vote now scheduled for June 2023.