Tribal fighters in Yemen have taken over government buildings in the capital, Sanaa, including the headquarters of the ruling party, sources tell Al Jazeera.
Fighters were also said to be surrounding the building of the interior ministry, our correspondents reported on Tuesday.
"[The buildings are] very close to the house of the [Hashed] tribal leader [Sadiq al-Ahmar] that was almost damaged by the shelling of the last few days," Mohamed al-Qadhi, the correspondent for the Abu Dhabi newspaper The National, told Al Jazeera.
"People of the tribal leader have said they control it but we are getting reports that it was taken by another military brigade, and they said they will prevent fighters from attacking the house of al-Ahmar from this building."
At least 320 people have been killed in fighting in Yemen since protests calling for Ali Abdullah Saleh, the president, to end his 33-year rule started about four months ago, inspired by the popular uprisings that ended the reign of the long-standing rulers of Tunisia and Egypt.
On the second day of continuing street clashes between Saleh's security forces and Hashed tribesmen, hundreds of explosions were heard, several people killed and dozens injured in Sanaa on Tuesday.
The most intense fighting was in the Hasaba district, close to al-Ahmar's residence.
"There have been heavy clashes and confrontations. It is the most severe and the most clashes that have taken place in Sanaa since the two sides started clashing with one another," al-Qadhi, the Sanaa-based journalist, said.
"The tribal leader's supporters are concerned more with the places used to launch attacks on al-Ahmar and his supporters. So I think they are expanding their contol over several government builidngs."
A tenuous truce declared a few days ago to end street fighting between the two groups broke down, with a government official on Tuesday saying "the ceasefire agreement has ended".
In another incident, security forces reportedly shot dead at least two anti-government protesters in Yemen's second-largest city, Taiz, on Tuesday, witnesses said.
They said that security forces were attempting to prevent anyone from gathering in the city, firing on those who tried to do so.
Medics confirmed that at least two people had been killed.
Tuesday's deaths came after protesters said security forces smashed a four-month-long sit-in in Taiz on Monday, killing 21 protesters.
According to reports received by the UN, more than 50 protesters have been killed in Taiz since Sunday.
"The UN human rights office has received reports, which remain to be fully verified, that more than 50 people have been killed since Sunday in Taiz by Yemeni Army, Republican Guards and other government-affiliated elements," Navi Pillay, the UN human rights chief, said on Monday.
The violence in Sanaa and Taiz follows the killing of at least 30 people in air raids in the southern city of Zinjibar, which is now said to be controlled by fighters linked to al-Qaeda.
Monday's air attack appeared to be in response to the takeover of the city by 300 alleged al-Qaeda fighters and an overnight ambush that killed at least six Yemeni soldiers and injured dozens more who were travelling to the southern city.
"Civilians found a military car and an armoured vehicle. They were destroyed, and the bodies of six soldiers were found on the roadside," Ayman Mohamed Nasser, editor-in-chief of Attariq, Aden's main opposition paper, told the Reuters news agency by telephone.
Opposition leaders have accused Saleh of deliberately allowing Zinjibar, near a sea lane where about three million barrels of oil pass daily, to fall to al-Qaeda in a bid to show how chaotic Yemen would be without him.
The deal was aimed at stemming the growing chaos in Yemen, home to al-Qaeda fighters and neighbour to the world's biggest oil exporter, Saudi Arabia.
Source: Al Jazeera and agencies