It comes after last month's violent election that extended President Robert Mugabe's 28-year rule in the country.
The Group of Eight said it was deeply concerned by events in the southern African country and did not accept the legitimacy of any Zimbabwean government that failed to reflect the people's will.
Mr Mugabe was the only candidate in election after the opposition leader Morgan Tsvangirai pulled out, blaming state-sponsored violence against his supporters.
Earlier, the G8 leaders restated their target to halve greenhouse gas emissions by the middle of the century, but said this could happen only if economies like China and India also commit themselves.
Japan's Prime Minister Yasuo Fukuda, who is hosting the 2008 G8 summit, announced the deal after all-night negotiations.
Last year's G8 summit pledged only to 'seriously consider' the cuts. The leaders have also expressed serious concerns about the threat posed to the global economy by soaring oil prices.
But they said they remained positive about the long-term resilience of their economies, as long as countries resisted the introduction of trade barriers.
The G8 earlier agreed to bring oil producers and consumers together in a world energy forum to discuss output and prices.
