The party of Yemen's former president Ali Abdullah Saleh, a key ally of Shiite Huthi rebels, on Tuesday welcomed UN-brokered peace talks due to open in Switzerland at the weekend.

The General People's Congress said it had not yet received a formal invitation from the United Nations but the UN envoy met with party representatives in the rebel-held capital in late May as part of his efforts to convene the Geneva talks.

Saleh himself is under UN sanctions for his support for the rebels and did not take part in the meetings, party sources said.

The GPC "welcomes holding the Geneva conference for consultations between Yemeni political components without any preconditions from any group, with goodwill and under the patronage of the United Nations," its almotamar.net website said.

Saleh, who ruled for 33 years before being forced from power in 2012 after a bloody year-long uprising, threw the support of his loyalists in the army behind the Huthis in their offensive that forced his successor into exile in March.

He himself proposed Geneva as the venue for the talks as a compromise between rebel-held Sanaa and the Saudi capital Riyadh, where exiled President Abedrabbo Mansour Hadi has taken refuge.

His loyalists have been repeatedly targeted alongside the rebels in a Saudi-led air war launched in support of Hadi on March 26.

On Tuesday, coalition air strikes hit pro-Saleh troops and rebels across the capital before dawn, witnesses said.

Plumes of smoke were seen rising from the defence ministry which they jointly control.

Residents also reported air strikes in third city Taez and the eastern oil province of Marib -- both key battlegrounds -- and in the rebel heartland in Yemen's far north.

- Violence grips Aden -

In the south, fierce clashes continued on the northern and western outskirts of Aden, Yemen's second largest city under rebels' attack since late March.

Seven people were killed and at least 67 others, mostly civilians, wounded since Monday, health chief Al-Khader Laswar said, as several Aden neighbourhoods were subjected to rebel shelling with rockets and mortars.

Coalition warplanes struck positions of rebels who have been attempting to storm the Bir Ahmed district, a military source said.

In Daleh, eight southern fighters were killed when coalition warplanes mistakenly hit a military post overrun by the pro-government fighters, according to a source in the Popular Resistance group.

The peace talks are due to open in Geneva on Sunday afternoon.

They had initially been scheduled for May 28 but were postponed after Hadi demanded the rebels first withdraw from seized territory.

They will last two to three days and be held mostly behind closed doors, according to UN spokesman Ahmad Fawzi.

UN chief Ban Ki-moon, who will attend the opening, has urged all sides to join the talks without preconditions in a bid to end a conflict which has killed more than 2,000 people since March.

But the exiled president set new conditions in an interview broadcast on Monday, insisting the sole item for discussion would be implementation of a UN resolution demanding a rebel withdrawal.

"There will be no negotiations," Hadi told Al-Arabiya television.