The United Nations humanitarian chief Valarie Amos arrived in Syria on Wednesday and is headed to the embattled city of Homs, which has been under assault by Syrian government forces for over a month.

Activists and members of the Syrian opposition have accused President Bashar al-Assad of covering up atrocities in Homs, such as extrajudicial executions and torture. Additionally, thousands of people are reportedly trapped in the city without food and electricity, many living in buildings destroyed during four weeks of artillery shelling.

While in the city, the U.N. said it will urge all sides to allow unhindered access for humanitarian relief workers so they can evacuate the wounded and deliver essential supplies.

The Red Cross has been allowed to deliver aid to parts of Homs, but has continually been blocked from the devastated Bar Amr neighborhood, which is now under the control of the Syrian army.

Amos' visit comes amidst the latest military push by Assad's forces. On Tuesday night, Syrian forces bombed the bridge being used by refugees to escape into Lebanon. Thousands of Syrian civilians, some of them injured, have fled west to Lebanon from the Homs province and from other parts of the Syria.

The bridge was hit by artillery shells, Syrian activist Hadi Abdallah told Australia's ABC News, referring to the bridge in the village of Rableh that was used last week to carry foreign journalists to safety.

It can no longer be used. It was the main route used to transport the wounded.

The UN aid trip also corresponds with the latest proclamation from Assad, who vowed on Tuesday to crush the foreign terrorists responsible for the protests and violence in his country.

The Syrian people, who have in the past managed to crush foreign plots ... have again proven their capacity to defend the nation and to build a new Syria through their determination to pursue reforms along with the fight against foreign-backed terrorism, he told delegates from the Ukrainian parliament in Damascus.

Any country draws its strength from the backing of its people.

An estimated 7,500 people are believed to have been killed in nearly a year of violence in Syria., according to the U.N.

On Tuesday, President Barack Obama said that the United States would not engage with Assad militarily, despite the humanitarian crisis.

For us to take military action unilaterally, as some have suggested, or to think that somehow there is some simple solution, I think is a mistake, Obama said.

What happened in Libya was we mobilized the international community, had a U.N. Security Council mandate, had the full cooperation of the region, Arab states, and we knew that we could execute very effectively in a relatively short period of time. This is a much more complicated situation.