Riot police moved into the grounds using teargas and stun grenades in an operation which sent smoke rising from the compound and which they said was to disperse protesters throwing stones, metal bars and rubbish at the end of Friday noon prayers in the mosque, Islam's third holiest shrine.

There were also running exchanges of stones and stun grenades between police and protesters in the nearby alleys below the historically much-fought-over hilltop compound, where the mosque is situated and which is known to Jews as the Temple Mount and to Muslims as Haram al-Sharif.

Police said that 17 policemen had been taken to hospital with injuries while a Palestinian volunteer nurse who had helped to staff a clinic next to the mosque said he had counted 23 injured worshippers. None of the injuries were through to be serious. Police said that they had made 17 arrests.

The compound, combined with the Western Wall, the holiest place in Judaism, which lies below it, is in religious and political terms the most sensitive site in the Arab-Jewish conflict. The second intifada followed Ariel Sharon's decision to conduct a heavily policed walk on the compound in 2000. Earlier about 2,500 Israeli police had mounted a massive security operation around the Old City, barring cars from adjacent roads on its Arab East Jerusalem side and banning Palestinians under the age of 45 from entering in an attempt to prevent protests.

Shopkeepers in the main alley running through the Bab Hutta neighbourhood close to the mosque closed their steel shutters and retreated inside as armed riot police moved in groups of 20 to 30 down the street several times to fire stun grenades at protesters who sporadically threw stones.

One policeman was injured in the leg by a stun grenade which had been hurled back at police by protesters before exploding. Police said that about 150 protesters, including some teenagers who had managed to evade the age ban, barricaded themselves in the mosque after the initial clashes, triggering a standoff in which adult worshippers, including women and elderly men, remained inside while police negotiated with Muslim leaders.

The protesters were finally persuaded to leave peacefully after about 90 minutes by an Arab Knesset member, Talab al-Sana. Power had earlier been cut to the mosque to prevent loudspeakers being used for what police claimed was "incitement" to violent protests.

The immediate trigger for the dispute is a decision by the Israeli authorities to begin digging up the stone ramp formerly used for access to the Mugrabi Gate, which is normally used by tourists to enter the compound and has been controlled by the Israeli authorities since the Six Day War in 1967.

The work is the first stage of a plan to build a new raised walkway. This will replace the wooden walkway, which was erected three years ago beside the Western Wall after a storm damaged the original ramp.

In a move which the Israeli authorities say is normal whenever construction takes place in the area, archaologists are conducting a "salvage dig" , which has reignited repeated claims by Muslim leaders that excavations around the compound are threatening the foundations of the Al Aqsa Mosque. The Israeli government says this is merely a pretext for the protests.

King Abdullah of Jordan, who still has custodianship of the Muslim shrines, has described the work as a "blatant violation" and a " dangerous escalation ... These measures will only create an atmosphere that will not at all help in the success of efforts being undertaken to restore the peace process," he said.

The decision to undertake the work ­ and its timing ­ has also created dissent within the Israeli cabinet. The Prime Minister, Ehud Olmert, indicated the work would continue despite being urged ­ in a move which quickly became public ­ by the Defence Minister, Amir Peretz, for the work to stop pending further consultations. A subsequent statement by Mr Olmert's office said the work was was done "in complete co-ordination with all parties, including foreign countries, relevant Muslim officials and international bodies".

Some European diplomats have suggested that the perceived threat from excavations may be a lesser factor in the protests than a fear that the new walkway will give easier access to Israeli forces to the compound.

Leading Israeli archaeologists, including those at the Israel Antiques Authority, are adamant that there is no risk of damage to the mosques or the holy sites. The Israeli Foreign Minister, Tzipi Livni, accused " political extremists" of trying to "exploit this situation."

Amid the repeated sound of exploding stun grenades, one man, Zaki Dweik, 48, paraded four of them which he said he had collected in the area between the Al Aqsa Mosque and the Dome of the Rock where the main disturbances took place. "As soon as we finished the two Rakas (communal prayers) they rained down tear gas and stun grenades," he said.

Mickey Rosenfeld, the Israeli police spokesman, said yesterday that police had refrained from entering the mosque and that they had used minimal force, despite the stonethrowing and calls to begin violent protests at the end of noon prayers.

Jerusalem's holiest site

Nowhere in Jerusalem is more sensitive or religiously significant than the site is known to Jews as the Temple Mount and to Muslims as Harem al-Sharif, or Noble Sanctuary.

The site, a sprawling compound covering 35 acres of land in East Jerusalem's Old Town, is holy to Jews because it is the location of the First and Second Temple, as well as the rock on which Abraham offered his son as a sacrifice to God.

It is known in Jewish tradition as the "abode of God's presence".

It is also viewed as holy by Muslims, for whom it is the site of the Prophet Mohamed's first prayers and his ascent into heaven. Al Aqsa Mosque is the third holiest site in Islam.