China risks another "historical tragedy" like the Cultural Revolution unless it enacts political reforms, the nation's outgoing prime minister, Wen Jiabao, has warned, in his strongest public call for change to date.

But some suggested the remark was linked to his later swipe at the ambitious Chongqing party leader, Bo Xilai, whom critics accuse of adopting quasi-Maoist tactics reminiscent of that era. Bo was thought likely to rise to a top political position when a new generation of leaders takes over late this year, but has been hit by a scandal involving a key ally.

"We must press ahead with both economic reform and political structural reform, especially reform in the leadership system of our party and country," Wen said at his annual press briefing at the end of the yearly session of China's largely rubber-stamp parliament.

"Reform has reached a critical stage. Without successful political structural reform, it is impossible for us to fully institute economic structural reform and the gains we have made in this area may be lost.

"The new problems that have cropped up in China's society will not be fundamentally resolved, and such historical tragedies as the Cultural Revolution may happen again."

Hundreds of thousands died and millions were persecuted in the decade-long turmoil launched by Mao Zedong in 1966.

He did not indicate what kind of reforms he had in mind, but stressed that they would have to be "gradually and orderly" and conform with "national circumstances". He added that they would not be easy and would require "the consciousness, the support, the enthusiasm and creativity of our people".

Recent months have seen calls for reform from inside and outside the party, although most of those have focused on the need for economic change.

"Wen has been consistent – almost combative – on the issue of the need to use reform to protect the progress China has made. And he's also been strong in pushing the line that political reform of some sort is central to that task," said Russell Leigh Moses, a Beijing-based political observer.

In most cases his comments have been carried by only a handful of the Chinese media, suggesting to some that he is an isolated figure hampered by conservative colleagues. Others suggest he has merely paid lip service to liberal concerns.

"We don't know if he is a lone voice [on reform]," said Steve Tsang, an expert on elite politics at Nottingham University.

"He is the good cop, the soft face – which is good not just for him, but for the Communist party."

He added: "I would suspect [the Cultural Revolution reference] is a shot across the bows, to say Bo is down and let's keep him down."

Bo became nationally renowned thanks to an anti-gang crackdown and "red culture" campaign, with many suggesting he would be elevated to the top political body this autumn. But critics saw those as Maoist-style initiatives and some feared him as a potential strongman.

"Until Bo Xilai made waves in Chongqing and projected himself strongly and effectively as a powerful, charismatic leader, we have had a succession of leaders who have got duller and duller … [and] relied on the party apparatus to get things done. Bo Xilai went beyond the party apparatus in terms of his capacity to appeal to people," said Tsang.

The premier did not mention Bo by name. But when asked about the case of Wang Lijun, the former Chongqing police chief and close ally of Bo who is under investigation after apparently seeking to defect to the United States, Wen gave a clear rebuke.

"Over the years, successive governments and people in Chongqing made enormous efforts to promote reform and development and have achieved remarkable progress. The current party committee and government must seriously reflect on the Wang Lijun incident and the lessons from this incident," he said, before making another reference to the lessons learned from the cultural revolution.

Officials – including Bo himself – had insisted that the case was an isolated incident. Bo sought to fight back against critics at another press conference on the sidelines of the National People's Congress last week.