State radio and the government-controlled Herald newspaper quoted Mugabe Wednesday as saying he would soon announce a new Cabinet that the opposition would be welcome to join.
But The Herald said opposition leader Morgan Tsvangirai's party "does not want to come in, apparently."
Mugabe and Tsvangirai are deadlocked in power-sharing talks over how much control Mugabe should surrender.
State media said Mugabe made the announcement Tuesday after he officially opened the first parliament since disputed March elections, one dominated for the first time in Zimbabwe's history by opposition legislators.
The opposition lawmakers jeered Mugabe Tuesday as he opened the parliament, singing and chanting and sometimes drowning out his voice.
The rare show of defiance - broadcast live on national television - set the stage for a combative legislature, even as Mugabe and his political foes try to negotiate a power sharing arrangement after disputed elections.
Mugabe's speech could sometimes not be heard over the jeers of his opponents, who clapped and sang songs deriding him and the ZANU-PF. "ZANU is rotten. You are great liars," they sang.
"We are tired of you," they shouted.
Looking annoyed, Mugabe first raised his voice then raced through the final lines of a speech railing against the West for sanctions it has imposed on people and companies linked to him, including travel bans and asset freezes.
Mugabe has ruled Zimbabwe with increasing authoritarianism since declaring independence from its former colonizer, Britain, in 1980 and had turned parliament into a rubber-stamp body.
But, with the country in economic freefall, the opposition Movement for Democratic Change has gained a strong following in recent years and this March clinched a parliamentary majority, posing the most serious threat yet to the 84-year-old leader's decades-long rule.
Tuesday's raucous session may be a glimpse into a future of bitter debates and close votes in parliament.
Opposition legislators also presented a petition Tuesday pointing out that the opening of the parliament was "a clear breach" of the agreement that led to power-sharing talks.
It called Mugabe "the illegitimate usurper of the people's will."
The petition also condemned the arrests of opposition legislators. When parliamentarians reported Monday to be sworn in, two were arrested. A third opposition legislator who is on the team negotiating power-sharing was arrested at his home early Tuesday, the opposition reported.
Opposition spokesman Nelson Chamisa said the arrests are an attempt to subvert his party's slight majority in parliament.
Some 2,000 opposition activists remain jailed in Zimbabwe months after March 29 elections where they garnered more votes than Mugabe and his party.
Mugabe reacted violently, unleashing soldiers, police and militants accused of killing nearly 200 opposition members, breaking the limbs of thousands and forcing tens of thousands from their homes with fire attacks.
In March, Tsvangirai's Movement for Democratic Change won 100 of the 210 seats in parliament, upsetting ZANU-PF's long-held majority. Mugabe's party won 99 seats and a splinter opposition faction won 10. An independent who broke away from Mugabe's party has the remaining seat.
In parliament Monday, the opposition's Lovemore Moyo won the race for speaker by a surprising 110 votes to 98. The ballot was secret, but Moyo apparently got votes from both Mugabe's party and the splinter faction to win a post that puts him in charge of parliament's debate and schedule and gives him the power to appoint committee chairmen.
Parliament's first order of business will be to approve funds for government ministries and projects - a budget vote that normally would have been completed months ago. So government business will remain largely paralyzed until legislators meet again on Oct. 14.
If the opposition continues to win support from the splinter faction, it would have the simple majority needed to block those funds. But if there is deadlock, Mugabe could dissolve the assembly and rule by decree. It is unlikely the opposition could summon the two-thirds vote needed to impeach Mugabe.
Meanwhile, there is a standoff in the negotiations over how Tsvangirai and Mugabe would share power.
Tsvangirai beat Mugabe and two other candidates in presidential elections held alongside the legislative balloting, but did not gain the simple majority needed to avoid a runoff. Mugabe held a one-man runoff and declared himself victor despite Western condemnation.
The opposition blames Zimbabwe's crisis on Mugabe's increasingly autocratic and corrupt rule. Zimbabwe began unraveling after Mugabe ordered the often-violent seizures of white-owned commercial farms for landless blacks. Instead, most farms went to Cabinet ministers and generals who let the land lie fallow and destroyed the country's economic base.
Mugabe has repeatedly blamed his country's woes on European and U.S. sanctions, which he called illegal on Tuesday.
"Sanctions must go," he said, to cheers from his supporters. "They cannot last a day longer if we as Zimbabweans speak against them in deafening unison." The sanctions target people and companies linked to Mugabe with travel bans and asset freezes.
While they are meant to spare ordinary Zimbabweans, already suffering from chronic shortages of food, medication, electricity and water, Zimbabwean officials say the sanctions help discourage foreign investment, loans and aid.
More than a third of Zimbabweans depend of foreign food aid but Mugabe has barred charities for handing out the food, charging they were favoring opposition supporters. Opposition legislators on Tuesday called on Mugabe to honor his agreement to allow food to be distributed, signed as a prerequisite for the power-sharing talks.