MURSITPINAR, Turkey — The first contingent of Iraqi Kurdish fighters crossed the Turkish border and arrived in the besieged Syrian city of Kobani on Thursday, aiming to help fellow Kurds fight off the militants of the Islamic State, Syrian activists said.

The reinforcements, led by a small vanguard of about a dozen troops, are expected to number about 150 in all, providing badly needed assistance to the town’s defenders. A separate group of fighters from a pro-Western Syrian rebel group had arrived on Wednesday.

Kobani, just yards from the Turkish frontier, has become an emblem of the West’s confrontation with the Islamic State, which has seized control of a large swath of Syria and Iraq. A campaign of U.S.-led airstrikes is attempting to dislodge them from their positions around Kobani and elsewhere.

The British-based Syrian Observatory for Human Rights said the Iraqi Kurdish soldiers, or peshmerga, crossed into Syria around noon. The city was the scene of heavy overnight clashes, and Islamic State fighters have been trying to seize control of the nearest border crossing to Kobani.

Crowds made up mainly of Kurds braved wind and rain to cheer on the peshmerga as they passed through Turkish territory. The assault on Kobani has been going on for six weeks. An estimated 800 people have been killed, and tens of thousands of civilians have fled.