An army official in Tripoli said government supporters had fought loyalists of an Alawite sect with links to Hezbollah in the Bab al-Tebbaneh, Kobel and Jabal Mohsen neighbourhoods.
"One woman has died in her house near Bab al-Tebbaneh," he said, adding that about 7,000 people had fled the fighting.
He said that several people had been wounded in the fighting.
Opposition fighters had earlier seized much of Beirut after battles with government supporters.
Lebanese police have said that 44 civilians have been killed and 129 others injured in the fighting.
But the capital is now coming under the control of the army after opposition forces were ordered to stand down by their commanders.
Hezbollah, which heads the opposition, said it would end its takeover of west Beirut on Saturday, after the army overturned government measures against them.
"The opposition welcomes the army's decision and will proceed with the withdrawal of all its armed elements so that control of the capital is handed over to the military," an opposition statement said.
A statement from the army command called on "all parties" to end armed protest.
The fighting erupted after the government said it would take action against Hezbollah's communications network
The government also suspended the head of security at Beirut airport, citing his alleged sympathies to Hezbollah.
But Hezbollah said any action against its communications network, which played a crucial role in the group's 34-day war with Israel in 2006, was tantamount to declaring war.
It also called for the airport chief to be reinstated.
The violence that followed was the worst internal fighting since Lebanon's 1975-90 civil war.
After fierce fighting in Beirut, an army statement on Saturday said Brigadier-General Wafiq Shqeir, the head of security at the airport, would remain in his post "pending an investigation".
"As for the telecommunications network, the army will look into the issue in a manner that is not harmful to the public interest or the security of the resistance", it said, referring to Hezbollah.
The military's action followed a televised address by Fouad Siniora, the Lebanese prime minister, in which he accused Hezbollah of staging a coup, calling the Shia group's takeover a "poisonous sting" to democracy.
In his speech, Siniora's first public reaction to Hezbollah's takeover of west Beirut, he said Hezbollah's weapons could no longer be considered legitimate as they had been turned on Lebanese citizens.
"Hezbollah must realise that force of arms will not scare us or make us retreat," he said.
But analysts questioned what the government would be able to do about disarming Hezbollah.
Commenting on Siniora's speech, Hisham Jaber, a former Lebanese army general, told Al Jazeera: "For Hezbollah to give the government its weapons is a joke - the opposition does not trust this government."
Jaber said: "The army would risk being divided and they are not prepared to defend any government. The army is not supposed to protect the government."
In Beirut, 16 people were killed on Saturday, two of them at a funeral procession for an earlier victim of the fighting.
Hezbollah said it blamed Walid Jumblatt, the pro-government Druze leader, for the death of at least two of its members in Aley, east of Beirut.
Jumblatt admitted there had been "an unfortunate incident" in the predominantly Druze and Christian town, in which "three people" had been killed.
"Two bodies were found and turned over to the army," he said.
He did not admit his supporters were responsible, but said if unconfirmed reports that the victims had been tortured proved to be true, he would "personally take responsibility for it".
Relative calm had settled over most of west Beirut on Saturday, as people ventured out in the affected areas and cleaning crews swept away the debris.
The army was out in force manning roadblocks and far fewer armed men were on the streets, though the main road to the airport remained blocked for a fourth day and there were no incoming or outgoing flights.
Rula Amin, Al Jazeera's correspondent in Beirut, said the standoff between the US-backed government and the opposition was over for the time being.
"Hezbollah has already started pulling its supporters off the streets and by Monday the government should have revoked its decisions," she reported.
|Siniora said Hezbollah's weapons could no|
longer be considered legitimate [AFP]
But she said even though the government had tried to save face by deferring to the army, it had in reality still bowed to Hezbollah's demands.
"The truth is Hezbollah won and it got what it wanted - the government had been adamant that it won't revoke its decisions but now they will," she said.
"It's embarrassing to the government and to the March 14 coalition not only because they had to back off on these decisions, but also because they lost to Hezbollah so quickly."
Washington pointed the finger at Iran and Syria - both of which back Hezbollah - for the violence, saying they must be held to account.
"The United States is consulting with other governments in the region and with the UN Security Council about measures that must be taken to hold those responsible for the violence in Beirut accountable," the White House said.
Arab foreign ministers are due to hold an emergency meeting on Sunday to discuss the crisis.