Sanaa, Yemen (CNN) -- Brief scuffles broke out in Yemen's capital on Friday at the end of a day of huge pro- and anti-government rallies, witnesses said.
At least four people were injured in Sanaa after tens of thousands of people turned out for the second straight week of dueling demonstrations.
The turnout illustrates the grinding tensions on the streets of the impoverished country, facing regular protests from people citing government corruption, a lack of political freedom, and high unemployment.
Pro-government backers gathered to support President Ali Abdullah Saleh and vowed to fight for him under all circumstances.
Chants of "People want Ali Abdullah Saleh" and "With our soul and blood, we support you, Saleh," rang out at the pro-government rally.
Saleh addressed his supporters briefly, thanking them for turning out and promising them he won't let them down.
"Rule in Yemen cannot be changed by force. Yemen is a democratic nation and means for change are available democratically," he said.
"I will sacrifice my blood and everything valuable to be for the sake of my great people."
Five miles away, anti-government protesters were in Sanaa's Change Square demanding Saleh's ouster.
The protesters were planning to march toward the presidential palace but decided not to because they felt that could stoke violence.
"This regime must understand that our protests will continue to be peaceful and we will not be tricked to use force," said Mohammed Qahtan, spokesman for the opposition Joint Meeting Parties JMP.
But later, thousands of anti-government protesters started marching from Change Square to Sitteen Road, chanting "Change must happen" "Saleh, Saleh, he will fall," and "The people must take control."
At one point, pro-government gangs blocked the road and started hurling rocks at them, and some anti-government protesters started throwing rocks back.
Eyewitnesses say at least four anti-government protesters were injured slightly in the very brief skirmishes. The anti-government protesters dispersed and ceased marching.
Mohammed Sabri, a spokesman for the opposition dialogue committee, questioned the sincerity of the pro-government protesters. He claims he has signed documents proving that Saleh's followers are getting paid to protest and said that this tactic will not stop Saleh from falling.
"This game will end very soon," he said.
In Aden, anti-government protesters removed photos and posters of Saleh from governmental institutions and meeting halls.
"We do not want to see his pictures anywhere in Aden. He is not the ruler of the people and he focuses more on his family," said activist Salma Abdul Khaleq.
The country has been wracked by a Shiite Muslim uprising, a U.S.-aided crackdown on al Qaeda operatives, and a looming shortage of water. It has endured violence and unrest on several fronts.
Britain has advised against travel to Yemen and is urging citizens "to leave now by commercial means."
"The political situation is volatile," the Foreign Office said.
"A rapid deterioration in the security situation is possible if negotiations between the President and the opposition breakdown. Routes in and out of Sanaa and the other major cities may be blocked and airports closed or inaccessible."
An explosion at an ammunition factory on Monday left 150 dead, and there have been months of demonstrations targeting Saleh.
There were clashes last weekend between government forces and al Qaeda in the Arabian Peninsula, al Qaeda's affiliate in Yemen. People on both sides were killed, security forces said.
Calls for Saleh's ouster have increased in recent weeks following revolutions in Egypt and Tunisia. Saleh has ruled since 1978.
Saleh has been fighting to hold onto power, arguing that he is best equipped to lead the fight against Islamists. He has been a staunch U.S. ally in the fight against al Qaeda in the Arabian Peninsula.
The president has said he accepts opposition demands for constitutional reforms and holding parliamentary elections by the end of the year. Saleh has also promised not to run for president in the next round of elections.
But he said as recently as Sunday he will not offer any more concessions, and he described the opposition as an alliance against the country's majority, according to Saba, the Yemen news agency. Opposition leaders rejected the president's comments.