The EU's verdict on the fairness of the elections will be crucial to a decision on whether it continues to ease sanctions against Zimbabwe, Ashton said in a statement.
The EU's foreign policy chief did not broach the issue of such sanctions in her statement. The EU slapped sanctions on Zimbabwe in 2002 after an election marked by fraud allegations. These include an arms embargo and travel ban on Mugabe and 19 of his closest allies. They have been renewed every year since.
President Robert Mugabe is to be sworn back into office soon after winning the 31 July election, extending - at age 89 - his 33-year rule, which dates back to independence from Britain.
The United States said earlier this week it believed the vote was flawed and did not plan to loosen its own sanctions.
Ashton said the 28-member European Union shared the "serious concerns" raised in the initial assessment of the election by the Southern African Development Community, African Union and domestic observers.
"The EU underlines the importance and need to continue strengthening reforms to ensure that future elections are fully transparent and credible as well as peaceful," she said.
"The EU will review its relations with Zimbabwe, taking account of all these factors."
Britain said on Thursday Mugabe's re-election could not be deemed credible without an independent investigation into allegations of voting irregularities.