Updated

Libyan leader Moammar Gadhafi's forces intensified their campaign to take strategic heights in a western mountain range and targeted a road that many people have used to flee the fighting in Libya, forcing the temporary closure of a border crossing to Tunisia.

Much of the fighting centered around the town of Yafrin, and residents and rebel fighters said Wednesday that Gadhafi forces were using Grad missiles and rockets in their nearly monthlong siege. Residents, trapped in their homes, were cut off from food and medical supplies, they said.

To the west of the contested Nafusa mountain range, which is home to ethnic Berbers, Libyan shelling forced the closure late Tuesday of the so-called Wazen passage, which is a route people fleeing Libya have used to get to neighboring Tunisia. Jaber Naluti, a volunteer who has been trying to assist people in the area, said seven rebels were killed.

Reports from the area said that some of the shells fell inside Tunisia.

Tunisian jet fighters flew over the area but didn't fire, witnesses said. They said the passage was reopened on Wednesday.

Although Gadhafi's forces control most of the west, rebels have linked up with the minority Berbers to keep his forces out of the highest points of the Nafusa mountains, denying them a military advantage.

Gadhafi, who has ruled Libya for more than 40 years, has been using his military and militias to try to put down an uprising that began in February to try to remove him from power.

Rebel forces has taken control of much of eastern Libya, operating out of headquarters in the coastal city of Benghazi. They also have been fighting to keep the town of Misrata, the opposition's only major stronghold in western Libya.

BelJassem, a citizen-turned-fighter from a Berber village near Yafrin, which is 75 miles (120 kilometers) southwest of Tripoli, said Gadhafi forces were shelling the town repeatedly.

"We dig trenches and hide in there at night," says BelJassem, who gave only his first name for fear of reprisals.

On the eastern front, rebels engaged in an hours-long firefight with Gadhafi loyalists, said Dr. Suleiman Refadi, who works at the Ajdabiya Hospital.

He told The Associated Press that the rebels killed 14 of Gadhafi's fighters and captured 30 near the oil town of Brega, which is about 50 miles (80 kilometers) southwest of Ajdabiya. Refadi said he treated five wounded rebels.

Refadi said the rebels were helped by NATO airstrikes, which destroyed eight vehicles carrying heavy artillery.

There was no way to independently confirm the report because journalists are not allowed beyond a checkpoint on the outskirts of Ajdabiya.

Also Wednesday, a U.N. official appealed for global assistance for some 2 million people displaced by the fighting.

The United Nations humanitarian coordinator for Libya said some 1.6 million people inside the North African country need aid because fighting has disrupted basic services and depleted food and medical stocks.

Coordinator Panos Moumtzis, who is based in Geneva, an additional 500,000 who have crossed borders to Tunisia, Egypt and elsewhere in the region also need humanitarian assistance.

Moumtzis said he was asking international donors for $408 million to fund aid for Libya through September.

Meanwhile, the International Criminal Court prosecutors warned Libyan officials they will be prosecuted if they attempt to cover up crimes by forces loyal to Gadhafi.

Prosecutors issued the warning in a letter to Libyan Foreign Minister Abdelati al-Obeidi.

The letter also formally informed him of Prosecutor Luis Moreno-Ocampo's request for arrest warrants for Gadhafi, his son Seif al-Islam Gadhafi, and intelligence chief Abdullah al-Sanoussi. The judges will now have to decide whether to issue arrest warrants.

Moreno-Ocampo on Monday accused the three Monday of murder and persecution for allegedly ordering, planning and participating in attacks on civilians.

The letter also underscored that the court has jurisdiction in Libya because its investigation was ordered by the UN Security Council — a contention the Libyan government has rejected.

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Associated Press reporters Maggie Michael contributed to this report from Cairo, Egypt, and Michelle Faul from Benghazi, Libya.