Thabo Mbeki, South Africa's president, has been mediating the talks which were called for by the Southern African Development Community after violent crackdowns on the opposition in March.
"Twenty meetings have been held so far and one of the issues that emerged is the urgency of constitutional amendment, given the constitutional obligation to hold presidential elections by March 2008," Chinamasa said.
The MDC had originally been pushing for an entirely new constitution that would guarantee basic freedoms and free elections, but relented when the president's powers to appoint members of parliament were curbed.
|"Six months before scheduled elections, Zimbabwe is closer than ever to complete collapse" |
International Crisis Group report
"As a confidence-building measure, we do not stand in the way of the constitutional amendment," Thokozani Khupe, the deputy leader for one of the two MDC factions, said.
"But we are in no way abandoning our principle for a new people-driven constitution."
She insisted that the MDC was pressing for the repeal of tough media and security laws that give police wider powers to open mail and monitor the internet.
Analysts say Mugabe, under international pressure to adopt democratic reforms or step down after 27 years in power, may use the bill to handpick a loyalist as his successor and rule from the sidelines.
The amendment also combines presidential and parliamentary elections for the first time in 2008, effectively reducing Mugabe's current term from six to five years, equivalent to the life of the Harare parliament.
The 83-year-old leader has said he will seek another term as president next year.
The political developments come as an influential think-tank warns that Zimbabwe faces collapse if the West does not get behind the South African-led talks.
"Six months before scheduled elections, Zimbabwe is closer than ever to complete collapse," the Brussels-based International Crisis Group (ICG) said in a report on Tuesday.
"It is critical that all international actors close ranks behind the Mbeki mediation."
For its part, the government, which ordered businesses to freeze prices of milk, bread and other items in June, said it was making progress in controlling Zimbabwe's soaring inflation rate.
Prices rose by 6,592.8 per cent in August, down from 7,634.8 per cent in July.